Light deflection device and optical device

ABSTRACT

An object of the present invention is to provide a light deflection device having a simple structure suitable for reducing the size and weight where a deflection angle can be increased. The object can be achieved with a light deflection device including: a light deflection element that deflects incident light in one direct to be emitted; a driving unit that drives the light deflection element; and a diffraction element that is disposed on a light emission side of the light deflection element in which a periodic structure pitch gradually changes from a center of deflection from the light deflection element toward an outside.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2019/013832 filed on Mar. 28, 2019, which claims priority under 35U.S.C. § 119(a) to Japanese Patent Application No. 2018-063851 filed onMar. 29, 2018, Japanese Patent Application No. 2018-141340 filed on Jul.27, 2018 and Japanese Patent Application No. 2018-184467 filed on Sep.28, 2018. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a light deflection device having asimple structure suitable for reducing the size and weight where adeflection angle can be increased, and an optical device including thelight deflection device.

2. Description of the Related Art

Currently, a laser light deflection technique is applied to variousfields. Examples of the light deflection technique include an aberrationcorrection system for free-space optical communication and a scanningsystem for laser radar.

In the related art, as a laser light deflector or a pointing opticalsystem, for example, a gimbal mirror or a galvanometer mirror has beenwidely used. These methods are direct and simple methods because themirror is mechanically moved to control a direction of laser light.

In addition, as a configuration of the light deflector, a configurationin which the deflection angle is extended using a liquid crystal prismincluding a liquid crystal layer having a prism shape is also known.

As techniques of the related art relating to the liquid crystal prism,for example, techniques described in JP1994-194695A (JP-H6-194695A) andJP1995-092507A (JP-H7-092507A), and a technique (for example,P2003-295153A) of combining a liquid crystal layer and a wedge-shapedprism are present.

SUMMARY OF THE INVENTION

However, in the method of the related art, it is necessary to control arelatively large mirror along with a large physical operation.Therefore, there is a problem in that the method is not suitable for asystem requiring a reduction in size and weight or for a use requiringlow power consumption.

In addition, the liquid crystal prism including a liquid crystal layerhaving a prism shape has a problem in that the manufacturing process iscomplicated and the control is difficult.

Further, in a method of using a wedge-shaped prism as liquid crystal, itis necessary that the wedge-shaped prism has a thickness to some extent,and there is a problem in that this method is not necessarily suitablein a case where a reduction in weight and size is required.

An object of the present invention is to solve the problems of therelated art and to provide: a light deflection device having a simplestructure suitable for reducing the size and weight where a deflectionangle can be increased, and an optical device including the lightdeflection device.

In order to achieve the object, a light deflection device according tothe present invention has the following configurations.

[1] A light deflection device comprising:

a light deflection element that deflects incident light to be emitted;

a driving unit that drives the light deflection element; and

a diffraction element that is disposed on a light emission side of thelight deflection element in which a periodic structure pitch graduallychanges from a center of deflection from the light deflection elementtoward an outside.

[2] The light deflection device according to [1],

in which the light deflection element is a liquid crystal optical phasemodulation element.

[3] The light deflection device according to [1],

in which the light deflection element is a MEMS light deflectionelement.

[4] The light deflection device according to any one of [1] to [3],

in which the diffraction element is a liquid crystal diffractionelement.

[5] The light deflection device according to [4],

in which the liquid crystal diffraction element includes anoptically-anisotropic layer that is formed using a composition includinga liquid crystal compound and has a liquid crystal alignment pattern inwhich a direction of an optical axis derived from the liquid crystalcompound changes while continuously rotating in at least one in-planedirection.

[6] The light deflection device according to [5],

in which the liquid crystal alignment pattern of theoptically-anisotropic layer is a concentric circular pattern having aconcentric circular shape where the in-plane direction in which thedirection of the optical axis derived from the liquid crystal compoundchanges while continuously rotating moves from an inside toward anoutside.

[7] The light deflection device according to [5] or [6],

in which the optically-anisotropic layer includes a liquid crystalcompound that is twisted and aligned along a helical axis extending in athickness direction.

[8] The light deflection device according to [7],

in which the liquid crystal diffraction element includes twooptically-anisotropic layers having opposite twisted directions in whichthe liquid crystal compound is twisted and aligned along a helical axisextending in a thickness direction.

[9] The light deflection device according to [8],

in which the optically-anisotropic layer in which the liquid crystalcompound is not twisted and aligned is provided between the twooptically-anisotropic layers.

[10] The light deflection device according to any one of [4] to [9],comprising:

a λ/4 plate.

[11] The light deflection device according to [10],

in which the λ/4 plate is provided between the light deflection elementand the liquid crystal diffraction element.

[12] The light deflection device according to any one of [1] to [3],

in which the diffraction element is a hologram diffraction element.

[13] The light deflection device according to any one of [1] to [3],

in which the diffraction element is a surface relief diffractionelement.

[14] The light deflection device according to any one of [1] to [3],

in which the diffraction element includes a transparent substrate thatis formed of an inorganic material and an uneven pattern that is formedof a plurality of protrusions.

[15] The light deflection device according to any one of [1] to [14],comprising:

a light collecting element that is provided upstream of the diffractionelement in a light traveling direction.

[16] The light deflection device according to [15],

wherein the light collecting element is provided upstream of the lightdeflection element in the light traveling direction.

[17] An optical device comprising:

the light deflection device according to any one of [1] to [16];

a light source that emits light to the light deflection element of thelight deflection device; and

a light-receiving element.

According to an aspect of the present invention, it is possible toprovide a light deflection device having a simple structure suitable forreducing the size and weight where a deflection angle can be increased,and an optical device including the light deflection device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing an example of a light deflectiondevice according to the present invention.

FIG. 2 is a conceptual diagram showing another example of the lightdeflection device according to the present invention.

FIG. 3 is a conceptual diagram showing an action of the light deflectiondevice shown in FIG. 1 .

FIG. 4 is a conceptual diagram showing a liquid crystal optical phasemodulation element.

FIG. 5 is a conceptual diagram showing a liquid crystal diffractionelement.

FIG. 6 is a schematic plan view showing an optically-anisotropic layer.

FIG. 7 is a conceptual diagram showing an action of theoptically-anisotropic layer.

FIG. 8 is a conceptual diagram showing an action of theoptically-anisotropic layer.

FIG. 9 is a conceptual diagram showing an action of theoptically-anisotropic layer.

FIG. 10 is a schematic plan view showing another example of theoptically-anisotropic layer.

FIG. 11 is a conceptual diagram showing an exposure device that exposesan alignment film.

FIG. 12 is a conceptual diagram showing another example of the exposuredevice that exposes an alignment film.

FIG. 13 is a conceptual diagram showing still another example of thelight deflection device according to the present invention.

FIG. 14 is a conceptual diagram showing an optically-anisotropic layeraccording to an example of the present invention.

FIG. 15 is a conceptual diagram showing an optically-anisotropic layeraccording to an example of the present invention.

FIG. 16 is a conceptual diagram showing an action of an example of thelight deflection device according to the present invention.

FIG. 17 is a diagram conceptually showing an example of an opticaldevice according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a light deflection device according to an embodiment of thepresent invention will be described with reference to the drawings.

In each of the drawings, for easy visual recognition, the reduced scaleof components is different from the actual scale.

In the present specification, numerical ranges represented by “to”include numerical values before and after “to” as lower limit values andupper limit values.

In addition, “perpendicular” or “parallel” regarding an angle representsa range of the exact angle±10°.

In the present specification, Re(λ) represents an in-plane retardationat a wavelength λ. Unless specified otherwise, the wavelength λ refersto 550 nm.

In the present specification, Re(λ) is a value measured at thewavelength λ using AxoScan (manufactured by Axometrics, Inc.). Byinputting an average refractive index ((nx+ny+nz)/3) and a thickness (d(μm)) to AxoScan, the following expressions can be calculated.

Slow Axis Direction (°)Re(λ)=R0(λ)R0(λ) is expressed as a numerical value calculated by AxoScan andrepresents Re(λ).

(Light Deflection Device)

A configuration of the light deflection device according to theembodiment of the present invention will be described using conceptualdiagrams of FIGS. 1 to 3 .

As shown in FIG. 1 , a light deflection device 100 according to theembodiment of the present invention includes a collecting lens 131, aliquid crystal optical phase modulation element 101, a λ/4 plate 111,and a liquid crystal diffraction element 121 in order from the upstreamside in a traveling direction of light (light beam). The liquid crystaloptical phase modulation element 101 is the light deflection elementaccording to the embodiment of the present invention and is connected toa drive unit 141.

In the following description, the upstream and the downstream refer tothe upstream and the downstream in the light traveling direction.

The λ/4 plate 111 and the liquid crystal diffraction element 121 aredisposed on an emission side (downstream) of the liquid crystal opticalphase modulation element 101 as shown in FIG. 1 .

The liquid crystal optical phase modulation element 101, the λ/4 plate111, and the liquid crystal diffraction element 121 may be disposed incontact with each other as shown in FIG. 1 , and may be further fixedusing an adhesive or the like.

In addition, even in a case where the liquid crystal optical phasemodulation element 101, the λ/4 plate 111, and the liquid crystaldiffraction element 121 are disposed to be spaced at an interval 102such that they do not deviate from a deflection angle of light emittedfrom the liquid crystal optical phase modulation element 101 as shown inFIG. 2 , the same effects as those of the present invention can beobtained.

Depending on the kind of the light, the light may generate heat duringpassing. By providing the interval 102, a problem caused in a case wherethe heat generated from the light during passing melts the adhesive orthe like used for fixing the liquid crystal optical phase modulationelement 101 and the λ/4 plate 111 and fixing the λ/4 plate 111 and theliquid crystal diffraction element 121 can be avoided. The interval 102is preferably 0.1 to 30 mm.

In a case where the interval 102 is provided, an incidence surface 103of the liquid crystal diffraction element 121 is in contact with an airlayer. Therefore, optionally, a non-reflective coating may be formed onan emission surface 161 or the incidence surface 103.

FIG. 3 is a conceptual diagram showing an action of the light deflectiondevice 100 according to the embodiment of the present invention.

As shown in FIG. 3 , the liquid crystal optical phase modulation element101 deflects incidence light 151 emitted from a light source (not shown)by a predetermined angle±0 (refer to a broken line).

The incidence light 151 is linearly polarized light in a directionindicated by an arrow 171 in the drawing. This linearly polarized lightis P polarized light with respect to the emission surface 161 of theliquid crystal diffraction element 121 in a direction parallel to thecross-sectional view shown in FIG. 3 .

In the present invention, S polarized light may be used as the incidencelight 151. This configuration can be handled by changing a part of theconfiguration of the liquid crystal optical phase modulation element101.

The light deflected from the liquid crystal optical phase modulationelement 101 is diffracted by the liquid crystal diffraction element 121such that the deflection angle is extended.

In FIG. 3 , a case where an angle θ of deflection from the liquidcrystal optical phase modulation element 101 is a counterclockwisedirection is set as a positive direction, and a maximum value in avariable range of the angle θ in the liquid crystal optical phasemodulation element 101 is set as a maximum deflection angle θmax. In thelight deflection device 100 according to the embodiment of the presentinvention, a periodic structure pitch (rotation period p describedbelow) in an optically-anisotropic layer 14 of the liquid crystaldiffraction element 121 described below is determined such that, in acase where light having the maximum deflection angle θmax is incidentinto the liquid crystal diffraction element 121, an emission angle is adesired maximum emission angle θmaxout in the light deflection device10.

As a result, even in a case where the maximum deflection angle θmax ofthe liquid crystal optical phase modulation element 101 decreases, themaximum deflection angle θmax of the liquid crystal optical phasemodulation element 101 can be extended to the desired maximum emissionangle θmaxout in the light deflection device 10 by the liquid crystaldiffraction element 121.

Likewise, even in a case where the angle θ is a negative direction, thatis, a clockwise direction, by determining the periodic structure pitchsuch that the emission angle at the maximum deflection angle θmax as themaximum value in a variable range of the angle θ is the desired maximumemission angle θmaxout in the light deflection device 10, the maximumdeflection angle θmax can be extended to the desired maximum emissionangle θmaxout.

Although described in detail below, in the liquid crystal diffractionelement 121, as the periodic structure pitch decreases, the diffractionangle increases. In addition, in the light deflection device 100, inorder to increase the deflection angle of emitted light, the diffractionangle of the liquid crystal diffraction element 121 gradually decreasesfrom the center of deflection (deflection orientation) from the liquidcrystal optical phase modulation element 101 toward the outside (bothend portions).

This implies that a relationship of pa<pb<pc is satisfied, where pa, pb,and pc represent periodic structure pitches (rotation periods p) ofregions 121 a, 121 b, and 121 c of the liquid crystal diffractionelement 121, respectively. Likewise, a relationship of pe<pd<pc issatisfied, where pd and pe represent periodic structure pitches ofregions 121 d and 121 e, respectively.

This way, in a case where the absolute value of the angle θ is between 0and the maximum deflection angle θmax and the angle θ of light emittedfrom the liquid crystal optical phase modulation element 101 is small,the periodic structure pitch is set to be large such that the light isslightly diffracted in the liquid crystal diffraction element 121. Inaddition, the angle θ of light emitted from the liquid crystal opticalphase modulation element 101 approaches the maximum deflection angleθmax, the periodic structure pitch gradually decreases such that thelight is largely diffracted in the liquid crystal diffraction element121.

As a result, the angle range of emitted light of the liquid crystaloptical phase modulation element is ±θmax, whereas the emission angle oflight emitted from the liquid crystal diffraction element 121 isextended to ±θmaxout.

Here, in a case where an incidence angle of light before being incidentinto the liquid crystal diffraction element 121 is represented by θ1, arefractive index of a medium on the incidence side is represented by n1,an emission angle of light emitted from the liquid crystal diffractionelement 121 is represented by θ2, a refractive index of a medium on theemission side is represented by n2, a wavelength of light is representedby λ, the periodic structure pitch of the liquid crystal diffractionelement is represented by p, and a diffraction order is represented bym, these values are associated with each other by the followingExpression (101).n1·sin θ1−n2·sin θ2=m·λ/p  (101)

As described below, by changing the periodic structure pitch p (rotationperiod p) of the liquid crystal diffraction element 121, the angle ofemitted light from the liquid crystal diffraction element 121 can bechanged.

In consideration of Snell's law, the absolute value of the final angleof emission from air can be extended to about 80°. Therefore, the angleθ can be extended up to a significantly large angle. In addition, bycontinuously changing the periodic structure pitch of the liquid crystaldiffraction element 121, that is, the rotation period p of theoptically-anisotropic layer 14 in a plane, light can be continuouslyemitted in any direction.

(Collecting Lens)

As described above, the light deflection device 100 includes thecollecting lens 131 as the light collecting element according to theembodiment of the present invention, the liquid crystal optical phasemodulation element 101, the λ/4 plate 111, and the liquid crystaldiffraction element 121 in order from the upstream side in the lighttraveling direction.

The collecting lens 131 is a well-known collecting lens and slightlycollects light incident into the liquid crystal optical phase modulationelement 101.

In the light deflection device 100 according to the embodiment of thepresent invention, the collecting lens 131 is provided as a preferableaspect. The light deflection device 100 according to the embodiment ofthe present invention includes the collecting lens 131 such that light(light beam) emitted from the light deflection device 100 (liquidcrystal diffraction element 121) can be converted into appropriateparallel light to improve straightness. The action of the collectinglens 131 will be described below in detail.

In the present invention, the light collecting element is not limited tothe collecting lens 131, and all the well-known optical elements thatcan collect light (light beam) can be used.

(Light Deflection Element)

[Liquid Crystal Optical Phase Modulation Element]

The structure of the liquid crystal optical phase modulation element 101will be described.

FIG. 4 is a cross-sectional view showing an example of the structure ofthe liquid crystal optical phase modulation element according to theembodiment of the present invention. Here, as the liquid crystal opticalphase modulation element described herein as an example, a liquidcrystal optical phase modulation element according to Example 1described in JP2003-295153A is adopted. In the present invention, theliquid crystal optical phase modulation element is not limited to theexample shown in the drawing, and all the liquid crystal optical phasemodulation elements used as a light deflection element can be used.

In FIG. 4 , a nematic liquid crystal layer 501 as an example of theliquid crystal layer is homogeneously aligned by an alignment layer 209that is formed to cover a composite electrode 211 of a first transparentsubstrate 201 and an alignment layer 209 that is formed to cover acommon electrode 213 of a second transparent substrate 203 in the liquidcrystal optical phase modulation element 101 such that a tilt angle γ ofa director 207 of a p-type (positive) liquid crystal molecule duringnon-application of an electric field is 5° or less.

In the liquid crystal optical phase modulation element 101 shown in FIG.4 , the incidence light 151 as the linearly polarized light in thedirection indicated by the arrow 171 is converted into linearlypolarized light parallel to a light deflection direction from the liquidcrystal optical phase modulation element 101. The incidence light 151 isP polarized light in case of being seen from the emission surface 161 ofthe liquid crystal diffraction element 121.

The first transparent substrate 201 and the second transparent substrate203 are fixed through a spacer (not shown) such that the nematic liquidcrystal layer 501 has a predetermined thickness of several micrometersto several tens of micrometers.

In addition, although not shown in FIG. 4 , in order to preventshort-circuit between the composite electrode 211 and the commonelectrode 213, a transparent insulating film formed of tantalumpentoxide, silicon dioxide, or the like may be formed on at least one ofthe composite electrode 211 or the common electrode 213. In addition, itis desirable that a multi-layer film consisting of a high refractiveindex film and a low refractive index film is used as the transparentinsulating film to improve transmittance.

The common electrode 213 formed on the second transparent substrate 203may be a full-surface electrode formed of a transparent conductive film.

With the above-described structure, different voltages can be applied tothe transparent electrodes. Therefore, by applying an electric fieldsuch that an in-plane distribution of the directors 207 of the liquidcrystal molecules is controlled to a predetermined refractive indexdistribution, incidence light can be deflected by a predetermined angleθ to be emitted due to the lens effect.

This principle is known as a liquid crystal lens, and the same effectscan be obtained even with various structures other than the presentaspect.

The light deflection device 100 shown in FIG. 1 includes the singleliquid crystal optical phase modulation element 101, but the presentinvention is not limited thereto. The light deflection device 100 mayinclude a plurality of liquid crystal optical phase modulation elements101.

In addition, in the liquid crystal optical phase modulation element 101,an alignment direction of a liquid crystal cell (liquid crystalcompound) may be parallel or vertical. In a case where the alignmentdirection of the liquid crystal cell is parallel, this configurationcontributes to an increase in maximum deflection angle θmax and alsocontributes to an extension in deflection angle from the liquid crystaloptical phase modulation element 101, that is, in deflection angle fromthe light deflection device 100.

(Drive Unit)

The drive unit 141 is connected to the liquid crystal optical phasemodulation element 101.

The drive unit 141 is a well-known drive unit that drives the liquidcrystal optical phase modulation element 101 according to theconfiguration of the liquid crystal optical phase modulation element101.

[λ/4 Plate]

The λ/4 plate 111 is a well-known λ/4 plate (¼ phase difference plate)that converts linearly polarized light deflected from the liquid crystaloptical phase modulation element 101 into circularly polarized light.

As the λ/4 plate 111, a well-known λ/4 plate can be used without anyparticular limitation. Accordingly, the λ/4 plate 111 may be derivedfrom a polymer or may be derived from liquid crystal.

(Diffraction Element)

[Liquid Crystal Diffraction Element]

FIG. 5 conceptually shows the liquid crystal diffraction element 121.FIG. 5 is a diagram showing the liquid crystal diffraction element 121in case of being in the same direction as that of FIGS. 1 to 3 , and isa side view showing the liquid crystal diffraction element 121.

The liquid crystal diffraction element 121 has a sheet shape andincludes a support 12, an alignment film 13, and anoptically-anisotropic layer 14.

As described above, the liquid crystal diffraction element 121 diffractslight deflected from the liquid crystal optical phase modulation element101 in a deflection direction from the liquid crystal optical phasemodulation element such that the light deflected from the liquid crystaloptical phase modulation element 101 is further deflected. In the lightdeflection device 100, by using the liquid crystal optical phasemodulation element 101 in combination with the liquid crystaldiffraction element 121, light can be deflected at a deflection angle ofthe maximum emission angle θmaxout that is significantly more than themaximum deflection angle θmax of the liquid crystal optical phasemodulation element 101.

In the example shown in the drawing, a sheet surface direction of theliquid crystal diffraction element 121 is defined as “x-y direction”,and a thickness direction is defined as “z direction”. In FIG. 5 , ahorizontal direction is a direction (axis A direction described below)in which an optical axis derived from a liquid crystal compound rotatesin one direction, and this direction is a x direction. Accordingly a ydirection is a direction perpendicular to the paper plane of FIG. 5 .

In addition, in FIGS. 1 to 3 , the up-down direction corresponds to thex direction, a direction perpendicular to the paper plane corresponds tothe y direction, and the horizontal direction corresponds to the zdirection. The x direction matches the deflection direction from theliquid crystal optical phase modulation element 101. Regarding thispoint, the same can also be applied to FIG. 13 described below.

In FIGS. 1 to 3 , the liquid crystal diffraction element 121 is planar.However, the liquid crystal diffraction element 121 may be curvedwithout being limited to being planar.

<Support>

As the support 12, various sheet-shaped materials (films or plate-shapedmaterials) can be used as long as they can support the alignment filmand the optically-anisotropic layer.

As the support 12, a transparent support is preferable, and examplesthereof include a polyacrylic resin film such as polymethylmethacrylate, a cellulose resin film such as cellulose triacetate, and acycloolefin polymer film. Examples of the cycloolefin polymer filminclude trade name “ARTON”, manufactured by JSR Corporation and tradename “ZEONOR”, manufactured by Zeon Corporation).

The support 12 may be a flexible film or may be a non-flexible substratesuch as a glass substrate.

<Alignment Film>

In the liquid crystal diffraction element 121, the alignment film 13 isformed on a surface of the support 12.

The alignment film 13 is an alignment film for aligning a liquid crystalcompound 20 to a predetermined liquid crystal alignment pattern duringthe formation of the optically-anisotropic layer 14.

Although described below, in the liquid crystal diffraction element 121,the optically-anisotropic layer 14 has a liquid crystal alignmentpattern in which a direction of an optical axis 22 derived from theliquid crystal compound 20 changes while continuously rotating in onein-plane direction. Accordingly, the alignment film 13 of the liquidcrystal diffraction element 121 is formed such that theoptically-anisotropic layer 14 can form the liquid crystal alignmentpattern.

In the optically-anisotropic layer 14 of the liquid crystal diffractionelement 121, in the liquid crystal alignment pattern, a length overwhich the direction of the optical axis 22 rotates by 180° in thein-plane direction (the direction along the axis A described below) inwhich the direction of the optical axis 22 changes while continuouslyrotating is set as a single period A (the rotation period p of theoptical axis 22). In the optically-anisotropic layer 14 of the lightdeflection device 100 according to the embodiment of the presentinvention, the single period gradually decreases from the center ofdeflection (deflection orientation (deflection direction)) from theliquid crystal optical phase modulation element 101 toward the outside.In addition, the rotation direction of the optical axis of the liquidcrystal compound 20 is reversed in the direction along the axis A (arrowX direction) at the center of deflection from the liquid crystal opticalphase modulation element 101. Accordingly, the alignment film 13 of theliquid crystal diffraction element 121 is formed such that theoptically-anisotropic layer 14 can form the liquid crystal alignmentpattern.

As the alignment film 13, various well-known films can be used.

Examples of the alignment film 13 of the optically-anisotropic layer 14include a rubbed film formed of an organic compound such as a polymer,an obliquely deposited film formed of an inorganic compound, a filmhaving a microgroove, and a film formed by lamination ofLangmuir-Blodgett (LB) films formed with the Langmuir-Blodgett techniqueusing an organic compound such as ω-tricosanoic acid,dioctadecylmethylammonium chloride, or methyl stearate.

Examples of the alignment film 13 include a film obtained by rubbing asurface of a polymer layer. The rubbing treatment is performed byrubbing a surface of a polymer layer with paper or fabric in a givendirection multiple times. As the kind of the polymer used for thealignment film, for example, polyimide, polyvinyl alcohol, a polymerhaving a polymerizable group described in JP1997-152509A(JP-H9-152509A), or a vertical alignment film such as JP2005-097377A,JP2005-099228A, and JP2005-128503A can be preferably used.

The vertical alignment film described in the present invention refers toan alignment film in which a major axis of a molecule of thepolymerizable rod-shaped liquid crystal compound according to thepresent invention is aligned to be substantially perpendicular to arubbing direction of the vertical alignment film. The thickness of thealignment film is not necessarily large as long as it can provide thealignment function, and is preferably 0.01 to 5 μm and more preferably0.05 to 2 μm.

As the alignment film 13, a so-called photo-alignment film obtained byirradiating a photo-alignable material with polarized light ornon-polarized light can be used. That is, the photo-alignment film maybe prepared by applying the photo-alignable material to the support 12.

The irradiation of polarized light can be performed in a directionperpendicular or oblique to the photo-alignment film, and theirradiation of non-polarized light can be performed in a directionoblique to the photo-alignment film.

Preferable examples of the photo-alignable material used in thephoto-alignment film that can be used in the present invention include:an azo compound described in JP2006-285197A, JP2007-076839A,JP2007-138138A, JP2007-094071A, JP2007-121721A, JP2007-140465A,JP2007-156439A, JP2007-133184A, JP2009-109831A, JP3883848B, andJP4151746B; an aromatic ester compound described in JP2002-229039A; amaleimide- and/or alkenyl-substituted nadiimide compound having aphoto-alignable unit described in JP2002-265541A and JP2002-317013A; aphotocrosslinking silane derivative described in JP4205195B andJP4205198B, a photocrosslinking polyimide, polyamide, or ester describedin JP2003-520878A, JP2004-529220A, and JP4162850B; and aphotodimerizable compound, in particular, a cinnamate compound, achalcone compound, or a coumarin compound described in JP1997-118717A(JP-H9-118717A), JP1998-506420A (JP-H10-506420A), JP2003-505561A,WO2010/150748A, JP2013-177561A, and JP2014-12823A. Among these, an azocompound, a photocrosslinking polyimide, polyamide, ester, a cinnamatecompound, or a chalcone compound is more preferable.

In the present invention, the photo-alignment film is preferably used.

FIG. 11 is a schematic diagram showing an exposure device for analignment film, in which the photo-alignable material is applied to thesupport 12 and dried to form an alignment film and the alignment film isexposed to form an alignment pattern.

An exposure device 50 includes: a light source 54 including a laser 52;a beam splitter 56 that splits laser light 70 emitted from the laser 52into two beams 72A and 72B; mirrors 58A and 58B that are disposed onoptical paths of the splitted two beams 72A and 72B; and λ/4 plates 60Aand 60B.

Although not shown in the drawing, for example, the light source 64includes a polarizing plate and emits linearly polarized light P₀. Theλ/4 plates 60A and 60B have optic axes perpendicular to each other, theλ/4 plate 60A converts the linearly polarized light P₀ into rightcircularly polarized light P_(R), and the λ/4 plate 60B converts thelinearly polarized light P₀ into left circularly polarized light P_(L).

The support 12 including the alignment film 13 on which the alignmentpattern is not yet formed is disposed at an exposed portion, the twobeams 72A and 72B intersect and interfere each other on the alignmentfilm 13, and the alignment film 13 is irradiated with and exposed to theinterference light.

Due to the interference at this time, the polarization state of lightwith which the alignment film 13 is irradiated periodically changesaccording to interference fringes. As a result, an alignment pattern inwhich the alignment state periodically changes can be obtained.

In the exposure device 50, by changing an intersection angle β betweenthe two beams 72A and 72B, the period of the alignment pattern can bechanged. That is, by adjusting the intersection angle β in the exposuredevice 50, in the alignment pattern in which the optical axis 22 derivedfrom the liquid crystal compound 20 continuously rotates in the in-planedirection, the length of the single period (rotation period p) overwhich the optical axis 22 rotates by 180° in the in-plane direction inwhich the optical axis 22 rotates can be adjusted.

By forming the optically-anisotropic layer 14 described below on thealignment film having the pattern in which the alignment stateperiodically changes, the optically-anisotropic layer 14 having theliquid crystal alignment pattern corresponding to the period can beformed.

In addition, by rotating the optical axes of the λ/4 plates 60A and 60Bby 90°, respectively, the rotation direction of the optical axis 22 canbe reversed. Accordingly, by masking half of a surface of the alignmentfilm 13, performing exposure, masking the exposed region, rotating theoptical axes of the λ/4 plate 60A and the λ/4 plate 60B by 90°,respectively, and performing exposure, the rotation direction of theoptical axis 22 can be reversed at the center in the in-plane directionin which the optical axis 22 of the liquid crystal compound 20 rotates.

Further, by repeating the operations of adjusting the intersection angleβ of the beams 72A and 72B, masking an unnecessary region, andperforming exposure, the length of the single period (rotation period p)over which the optical axis 22 rotates by 180° can gradually decreasetoward the outside from the center in the in-plane direction in whichthe optical axis 22 rotates.

In addition, in order to expose the alignment film 13, an exposuredevice 80 conceptually shown in FIG. 12 is suitably used. The exposuredevice 80 shown in FIG. 12 is used to form a liquid crystal alignmentpattern having a concentric circular shape as shown in FIG. 10 .

An exposure device 80 includes: a light source 84 that includes a laser82; a polarization beam splitter 86 that divides the laser light Memitted from the laser 82 into S polarized light MS and P polarizedlight MP; a mirror 90A that is disposed on an optical path of the Ppolarized light MP; a mirror 90B that is disposed on an optical path ofthe S polarized light MS; a lens 92 (convex lens) that is disposed onthe optical path of the S polarized light MS; a polarization beamsplitter 94; and a λ/4 plate 96.

The P polarized light MP that is split by the polarization beam splitter86 is reflected from the mirror 90A to be incident into the polarizationbeam splitter 94. On the other hand, the S polarized light MS that issplit by the polarization beam splitter 86 is reflected from the mirror90B and is collected by the lens 92 to be incident into the polarizationbeam splitter 94.

The P polarized light MP and the S polarized light MS are multiplexed bythe polarization beam splitter 94, are converted into right circularlypolarized light and left circularly polarized light by the λ/4 plate 96depending on the polarization direction, and are incident into thealignment film 13 on the support 12.

Due to interference between the right circularly polarized light and theleft circularly polarized light, the polarization state of light withwhich the alignment film 13 is irradiated periodically changes accordingto interference fringes. The intersection angle between the rightcircularly polarized light and the left circularly polarized lightchanges from the inside to the outside of the concentric circle.Therefore, an exposure pattern in which the pitch changes from theinside to the outside can be obtained. As a result, in the alignmentfilm 13, a concentric circular alignment pattern in which the alignmentstate periodically changes can be obtained.

In the exposure device 80, the length of the single period (rotationperiod p) over which the optical axis 22 of the liquid crystal compound20 continuously rotates by 180° in the in-plane direction can becontrolled by changing the refractive power of the lens 92 (the F numberof the lens 92), the focal length of the lens 92, the distance betweenthe lens 92 and the alignment film 13, and the like.

In addition, by adjusting the refractive power of the lens 92 (the Fnumber of the lens 92), the length of the single period over which theoptical axis 22 rotates by 180° in the in-plane direction in which theoptical axis 22 continuously rotates can be changed. Specifically, thelength of the single period over which the optical axis 22 rotates by180° can be changed depending on the degree to which light transmittedthrough the lens 92 is collected for interference with parallel light.More specifically, in a case where the refractive power of the lens 92is weak, light is approximated to parallel light. Therefore, the lengthof the single period over which the optical axis 22 rotates by 180°gradually decreases from the inside toward the outside, and the F numberincreases. Conversely, in a case where the refractive power of the lens92 becomes stronger, the length of the single period over which theoptical axis 22 rotates by 180° rapidly decreases from the inside towardthe outside, and the F number decreases.

This way, the configuration of changing the length of the single period(rotation period p) over which the optical axis 22 rotates by 180° inthe in-plane direction in which the optical axis 22 continuously rotatescan also be used in the configuration shown in FIGS. 1 to 10 in whichthe optical axis 22 of the liquid crystal compound 20 continuouslyrotates only in the in-plane direction as the arrow X direction.

For example, by gradually decreasing the single period over which theoptical axis 22 rotates by 180° in the arrow X direction, an opticalelement that allows transmission of light to be collected can beobtained. In addition, by reversing the direction in which the opticalaxis 22 in the liquid crystal alignment pattern rotates by 180°, anoptical element that allows transmission of light to be diffused only inthe arrow X direction can be obtained. By reversing the turningdirection of incident circularly polarized light, an optical elementthat allows transmission of light to be diffused only in the arrow Xdirection can be obtained.

Further, depending on the uses of the optical element such as a casewhere it is desired to provide a light amount distribution intransmitted light, a configuration in which regions having partiallydifferent single periods over which the optical axis 22 rotates by 180°in the arrow X direction are provided can also be used instead of theconfiguration in which the length of the single period over which theoptical axis 22 rotates by 180° gradually changes in the arrow Xdirection. For example, as a method of partially changing the singleperiod over which the optical axis 22 rotates by 180°, for example, amethod of scanning and exposing the photo-alignment film to be patternedwhile freely changing a polarization direction of laser light to begathered can be used.

In the liquid crystal diffraction element 121, the alignment film 13 isprovided as a preferable aspect and is not an essential component.

For example, the following configuration can also be adopted, in which,by forming the alignment pattern on the support 12 using a method ofrubbing the support 12, a method of processing the support 12 with laserlight or the like, or the like, the optically-anisotropic layer 14 hasthe liquid crystal alignment pattern in which the direction of theoptical axis 22 derived from the liquid crystal compound 20 changeswhile continuously rotating in at least one in-plane direction.

<Optically-Anisotropic Layer>

In the liquid crystal diffraction element 121, the optically-anisotropiclayer 14 that is a cured layer of the liquid crystal compositionincluding the liquid crystal compound 20 is provided on a surface of thealignment film 13.

The optically-anisotropic layer 14 has a liquid crystal alignmentpattern in which the optical axis (slow axis) of the liquid crystalcompound is arranged in at least one in-plane direction of theoptically-anisotropic layer and in which the direction of the opticalaxis 22 of the liquid crystal compound 20 changes while rotating in thein-plane direction.

In the liquid crystal diffraction element 121 according to theembodiment, a retardation R (=Δn d1) of the optically-anisotropic layer14 in the thickness direction (in the drawing, the z direction) withrespect to light having the wavelength λ is 0.36λ to 0.64λ. Theretardation R is preferably 0.4λ to 0.6λ, more preferably 0.45λ to0.55λ, and still more preferably 0.5λ. Δn represents a birefringence ofthe optically-anisotropic layer 14, and dl represents a thickness. Forexample, in a case where light having a wavelength of 940 nm is assumedas incidence light, the retardation R with respect to the light having awavelength of 940 nm may be in a range of 338 to 602 nm and ispreferably 470 nm.

By having the retardation R, the optically-anisotropic layer 14 exhibitsa function as a λ/2 plate, that is, a function of imparting a phasedifference of 180° (=π=λ/2) between linearly polarized light componentsof incidence light perpendicular to each other.

The liquid crystal diffraction element 121 functions as a transmissiondiffraction grating. The principle in which the liquid crystaldiffraction element 121 functions as a diffraction grating will bedescribed with reference to FIGS. 5 and 6 .

FIG. 6 is a schematic plan view showing the optically-anisotropic layer14, that is, a diagram showing FIG. 5 in case of being seen from thetop.

As shown in FIGS. 5 and 6 , in the optically-anisotropic layer 14, theliquid crystal compound 20 is immobilized in the liquid crystalalignment pattern in which the optical axis 22 changes whilecontinuously changing in the in-plane direction. In the example shown inthe drawing, the optical axis 22 changes while continuously rotating inthe direction along the axis A in FIG. 6 that matches the arrow Xdirection. That is, the liquid crystal compound 20 is aligned such thatan angle between an in-plane component of the major axis (the axis ofextraordinary light: director) of the liquid crystal compound 20 definedas the optical axis 22 and the axis A changes while rotating.

As shown in FIG. 6 , in the optically-anisotropic layer 14, thedirection of the optical axis 22 of the liquid crystal compound 20 isthe same in the liquid crystal compound 20 in which that is arranged ina direction perpendicular to the axis A, that is, in an arrow ydirection. The optically-anisotropic layer 14 exhibits theabove-described general function as a λ/2 plate in regions having thesame direction of the optical axis 22 of the liquid crystal compound 20in the y direction.

The liquid crystal alignment pattern in which the direction of theoptical axis 22 changes while rotating is a pattern in which the liquidcrystal compound 20 is aligned and immobilized such that an anglebetween the optical axis 22 of the liquid crystal compound 20 arrangedalong the axis A and the axis A varies depending on positions in theaxis A direction and gradually changes from ϕ to ϕ+180° or ϕ−180°.

In the following description, as shown in FIG. 6 , the liquid crystalalignment pattern in which the optical axis 22 of the liquid crystalcompound 20 is parallel to a surface of the optically-anisotropic layer14, local regions (unit regions) where the direction of the optical axis22 is constant, that is, regions where the liquid crystal compound 20 isarranged in the arrow Y direction are arranged in the x directionperpendicular to the arrow y direction, and the direction of the opticalaxis 22 change while continuously rotating in the in-plane direction(the direction along the axis A) in the plurality of local regionsarranged in the arrow X direction will be referred to as “horizontalrotation alignment”.

“Changing while continuously rotating” may represent that regions thesame angle such as 30° rotate to be adjacent to each other in a range of0° to 180° (=0°) as shown in FIGS. 5 and 6 . In addition, a change inthe angle of the optical axis 22 in the axis A direction may be rotationat different angle intervals instead of a uniform angle interval. In thepresent invention, in a case where the average value of the directionsof the optical axes 22 in the unit region changes linearly at a constantratio, it can be said that the direction of the optical axis graduallychanges. However, a change in the slope of the optical axis between unitregions adjacent to each other in the axis A direction and havingdifferent slopes of the optical axes 22 is preferably 45° or less. It ispreferable that a change in slope between unit regions adjacent to eachother is as small as possible.

In the optically-anisotropic layer 14, the distance over which the anglebetween the optical axis 22 and the axis A in the axis A directionchanges from ϕ to ϕ+180° (returning to the original position), that is,the period over which the optical axis 22 rotates by 180° will bereferred to as “rotation period p”. The rotation period p is preferably0.5 to 5 μm. As the rotation period p decreases, the diffraction anglefrom the optically-anisotropic layer 14, that is, the liquid crystaldiffraction element 121 increases. Accordingly, the rotation period pmay be determined depending on a wavelength of incidence light into theliquid crystal diffraction element 121 and a desired emission angle.

With the above-described configuration of the optically-anisotropiclayer 14, the liquid crystal diffraction element 121 imparts a phasedifference of λ/2 and emits incidence light incident at an incidenceangle of 0°, that is, vertically incident light at an emission angle θ2.

That is, as shown in FIG. 7 described below, in a case where light lightL₁ of right circularly polarized light P_(R) is vertically incident intoa surface of the optically-anisotropic layer 14, light L₂ of leftcircularly polarized light P_(L) is emitted in a direction having anangle θ2 with respect to the normal direction. In other words, Lightbeing vertically incident into the surface of the optically-anisotropiclayer 14 is light being incident along the normal line of the surface.In addition, the light light L₁ of right circularly polarized lightP_(R) incident into the optically-anisotropic layer 14 will also bereferred to “incidence light light L₁”. Further, in the followingdescription, the light light L₁ of left circularly polarized light P_(L)emitted the optically-anisotropic layer will also be referred to“emitted light L₂”.

In the liquid crystal diffraction element 121, in a case where lighthaving a predetermined wavelength is incident, as the rotation period pof the optically-anisotropic layer 14 decreases, the diffraction angle,that is, the emission angle of the emitted light L₂ increases. Theemission angle of the emitted light L₂ is an angle between the normaldirection of the optically-anisotropic layer 14 and the emitted lightL₂.

The liquid crystal diffraction element 121 has different diffractionorientations for right circularly polarized light and left circularlypolarized light. Therefore, regarding the diffraction direction of theemitted light L₂ from the liquid crystal diffraction element 121, thestate of circularly polarized light to be incident into the liquidcrystal diffraction element 121 is controlled to be incident. That is,as in the example shown in the drawing, in a case where incidence lightis linearly polarized light, by inserting the λ/4 plate 111 to convertthe linearly polarized light into left circularly polarized light orright circularly polarized light, the orientation of diffraction oflight can be controlled to only one of the right or left side.

FIG. 7 is a diagram schematically showing the principle in which theincidence light light L₁ vertically incident into theoptically-anisotropic layer 14 is emitted at the predetermined emissionangle θ2. Hereinafter, the action of the optically-anisotropic layer 14will be described with reference to FIG. 7 .

First, a case where right circularly polarized light P_(R) having thewavelength λ is used as the incidence light light L₁ will be described.

The incidence light light L₁ as the right circularly polarized lightP_(R) transmits through the optically-anisotropic layer 14 to beimparted with a phase difference of λ/2 and is converted into leftcircularly polarized light P_(L).

In addition, in the optically-anisotropic layer 14, the absolute phaseof the incidence light light L₁ changes due to the optical axis 22 ofthe liquid crystal compound 20 in each of the unit regions (localregions). Here, in the optically-anisotropic layer 14, the direction ofthe optical axis 22 of the liquid crystal compound 20 changes whilerotating in the axis A direction (in this example, that matches thearrow X direction). Therefore, the amount of change in absolute phasevaries depending on the direction of the optical axis 22 of the liquidcrystal compound 20 at x coordinates (the position in the x direction)of a plane (x-y plane) of the optically-anisotropic layer 14 into whichincidence light is incident. In a region indicated by a broken line inFIG. 7 , the state where the amount of change in absolute phase variesdepending on x coordinates is schematically shown.

As shown in FIG. 7 , due to a shift of the absolute phase in a casewhere light passes through the optically-anisotropic layer 14, anequiphase surface 24 having an absolute phase with an angle with respectto the plane of the optically-anisotropic layer is formed. As a result,a bending force in a direction perpendicular to the equiphase surface 24is applied to the incidence light light L₁ incident from the normaldirection such that the traveling direction of the incidence light lightL₁ changes. That is, the incidence light light L₁ as the rightcircularly polarized light P_(R) is converted into left circularlypolarized light P_(L) after passing through the optically-anisotropiclayer 14, and is emitted from the optically-anisotropic layer 14 as theemitted light L₂ that travels in a direction having the angle θ2 withrespect to the normal direction.

As described above, in the liquid crystal diffraction element 121, theincidence light light L₁ incident in the normal direction perpendicularto the plane of the liquid crystal diffraction element 121 is emitted asthe emitted light L₂ in a direction different from the normal direction.

By changing the rotation period p of the direction of the optical axisin the liquid crystal alignment pattern of the optically-anisotropiclayer 14, the slope of the emission angle can be changed. As therotation period p decreases, a high bending force can be applied to theincidence light, and thus the slope can be increased.

This way, due to the liquid crystal alignment pattern in theoptically-anisotropic layer 14, the amount of change in absolute phasecan be changed to change a wave surface of the incidence light.

In a case where the liquid crystal diffraction element 121 has theliquid crystal alignment pattern of the rotation period p that isuniform only in one direction, the conversion of the incidence lightlight L₁ into the emitted light L₂ based on the above-describedprinciple can be described as transmission diffraction.

The optically-anisotropic layer 14 functions as a transmissiondiffraction grating with respect to the incidence light light L₁, andthe incidence light light L₁ vertically incident into theoptically-anisotropic layer 14 is transmitted and diffracted as theemitted light (transmitted and diffracted light) L₂ having apredetermined diffraction angle θ2. In this case the followingExpression (1) that is an general expression for light diffraction issatisfied.n2 sin θ2−n1 sin θ1=mλ/p  Expression (1)Here, n1 represents a refractive index of a medium 1 on the incidencesurface side of a diffraction grating (here, the optically-anisotropiclayer 14), θ1 represents an incidence angle, n2 represents a refractiveindex of a medium 2 on the emission surface side of a diffractiongrating (here, the optically-anisotropic layer), θ1 represents adiffraction angle (emission angle), λ represents a wavelength, prepresents a rotation period, and m represents a diffraction order.Here, conditions are set such that the maximum diffraction efficiency isobtained at m=1. In addition, here, since incidence angle θ1=0°,Expression (1) is as follows.n2 sin θ02=λ/p  Expression (2)

FIG. 8 is a diagram schematically showing the diffraction phenomenonrepresented by Expression (2).

The optically-anisotropic layer 14 as a diffraction grating is disposedbetween the medium n1 and the medium n2.

The light light L₁ incident from the medium 1 side having a refractiveindex n1 into the optically-anisotropic layer 14 in the normal directionis diffracted due to the diffraction action from theoptically-anisotropic layer 14 and is emitted to the medium 2 sidehaving a refractive index n2. At this time, the emitted light L₂ emittedat the emission angle θ2 can be rephrased with the transmitted anddiffracted light L₂ having the diffraction angle θ2.

This way, the optically-anisotropic layer 14 obtained by performing thehorizontal rotation alignment on the liquid crystal compound 20 to beimmobilized functions as diffraction grating.

The wavelength λ of light that causes the diffraction effect to occurdue to the liquid crystal diffraction element 121 (optically-anisotropiclayer 14) may be in a ultraviolet range, a visible range, or an infraredrange or may be on an electromagnetic wave level.

At the same rotation period p, as the wavelength of the incidence lightincreases, the diffraction angle increases, and as the wavelength of theincidence light decreases, the diffraction angle decreases.

Although described below, as the liquid crystal compound 20, arod-shaped liquid crystal compound or a disk-shaped liquid crystalcompound can be used. In a case where the wavelength λ is 380 nm and therotation period p (μm) is in a range of 0.5<p<1, the disk-shaped liquidcrystal compound can obtain a higher diffraction efficiency than therod-shaped liquid crystal compound. In addition, in a case where thewavelength λ is 1100 nm and the rotation period p (μm) is in a range of2<p<5, the disk-shaped liquid crystal compound can obtain a higherdiffraction efficiency than the rod-shaped liquid crystal compound.

As shown in FIG. 7 , in a case where incidence light light L₁ of rightcircularly polarized light P_(R) is incident along the normal line ofthe surface of the liquid crystal diffraction element 121, emitted lightL₂ of left circularly polarized light P_(L) is emitted in a directionhaving the angle θ2 with respect to the normal direction.

On the other hand, in a case where left circularly polarized light isincident into the liquid crystal diffraction element 121 as incidencelight, the incidence light is converted into right circularly polarizedlight in the optically-anisotropic layer 14, and the traveling directionis changed by a bending force in a direction opposite to that of FIG. 7.

As shown in FIG. 9 , in a case where incidence light L₄₁ of randomlypolarized light is incident into the liquid crystal diffraction element121 (optically-anisotropic layer 14), a right circularly polarized lightP_(R) component in the incidence light L₄₁ is converted into leftcircularly polarized light P_(L) in the optically-anisotropic layer 14as described above, the traveling direction is changed by a bendingforce due to the liquid crystal alignment pattern, and the leftcircularly polarized light P_(L) transmits through theoptically-anisotropic layer to be emitted as first transmitted anddiffracted light L₄₂.

On the other hand, a left circularly polarized light P_(L) component inthe incidence light L₄₁ is converted into right circularly polarizedlight P_(R) in the optically-anisotropic layer 14, the travelingdirection is changed by a bending force in a direction opposite to thatof the left circularly polarized light converted from the rightcircularly polarized light, and the right circularly polarized lightP_(R) transmits through the optically-anisotropic layer 14 to be emittedas second transmitted and diffracted light L₄₃ from a surface oppositeto the liquid crystal diffraction element 121. The traveling directionsof the first transmitted and diffracted light L₄₂ and the secondtransmitted and diffracted light L₄₃ are substantially axisymmetric toeach other with respect to the normal line.

In the above description, the example in which incidence light isvertically incident into the optically-anisotropic layer. However, evenin a case where incidence light is obliquely incident into theoptically-anisotropic layer, the effect of transmission diffraction canalso be obtained.

In a case where incidence light is obliquely incident into theoptically-anisotropic layer, the rotation period may be designed inconsideration of the incidence angle θ1 such that Expression (1) issatisfied and the desired diffraction angle θ2 can be obtained.

As described above, in the light deflection device 100 according to theembodiment of the present invention, light deflected from the liquidcrystal optical phase modulation element 101 is refracted (diffracted)by the liquid crystal diffraction element 121 (optically-anisotropiclayer 14) such that the light can be deflected at a deflection angle ofthe maximum emission angle θmaxout that is significantly more than themaximum deflection angle θmax of the liquid crystal optical phasemodulation element 101.

The refraction (diffraction angle) of light from theoptically-anisotropic layer 14 increases as the single period over whichthe optical axis 22 of the liquid crystal compound 20 rotates by 180°,that is, the rotation period p decreases.

In addition, in a case where the deflection directions (turningdirections) of circularly polarized light to be incident are the same,the refraction direction of light from the optically-anisotropic layer14 is reversed by the rotation direction of the optical axis 22 of theliquid crystal compound 20.

That is, in a case where the incidence light light L₁ is rightcircularly polarized light P_(R) and the rotation direction of theoptical axis 22 is clockwise in the axis A direction (arrow X direction)from the emission surface side as shown in FIGS. 5 to 7 , the emittedlight L₂ is refracted, for example, in the axis A direction.

On the other hand, in a case where the incidence light light L₁ is rightcircularly polarized light P_(R) and the rotation direction of theoptical axis 22 is counterclockwise in the axis A direction from theemission surface side, the emitted light L₂ is refracted in a directionopposite to the axis A direction (refer to emitted light L₄₃ in FIG. 9).

Accordingly, in the optically-anisotropic layer 14 of the lightdeflection device 100 according to the embodiment of the presentinvention, the rotation period p of the optical axis 22 of the liquidcrystal compound 20 in the axis A direction gradually decreases from thecenter of deflection (deflection orientation) from the liquid crystaloptical phase modulation element 101 toward the outside. That is, theamount of refraction of light from the optically-anisotropic layer 14increases toward the outside in the deflection direction.

Further, in the optically-anisotropic layer 14 of the light deflectiondevice 100 according to the embodiment of the present invention, therotation direction of the optical axis 22 of the liquid crystal compound20 in the axis A direction is reversed at the center of deflection fromthe liquid crystal optical phase modulation element 101. For example, inthe example shown in the drawing, the rotation direction of the opticalaxis 22 in the axis A direction is set to be counterclockwise from theupstream side in the axis A direction to the center in the deflectiondirection, the rotation direction of the optical axis 22 is reversed atthe center of deflection, and the rotation direction of the optical axis22 is set to be clockwise from the center of deflection to thedownstream side in the axis A direction.

In a case where the light deflection device 100 according to theembodiment of the present invention has the above-describedconfiguration, light can be deflected at a deflection angle of themaximum emission angle θmaxout that is significantly more than themaximum deflection angle θmax of the liquid crystal optical phasemodulation element 101.

The rotation direction of the optical axis 22 is reversed at the centerof the optically-anisotropic layer 14 in the axis A direction (arrow Xdirection), that is, in the in-plane direction in which the optical axis22 rotates. That is, in the light deflection device 100, the center ofdeflection from the liquid crystal optical phase modulation element 101and the center of optically-anisotropic layer 14 in the axis A directionare matched to each other.

In the present invention, the rotation period p may decreasecontinuously or stepwise from the center of deflection toward theoutside.

<Formation of Optically-Anisotropic Layer>

For example, the optically-anisotropic layer 14 is formed using theliquid crystal composition including the liquid crystal compound.

In order to form the optically-anisotropic layer 14, the liquid crystalcomposition including the liquid crystal compound may include othercomponents such as a leveling agent, an alignment controller, apolymerization initiator, or an alignment assistant in addition to theliquid crystal compound. By forming an alignment film on the support,applying the liquid crystal composition to the alignment film, andcuring the applied liquid crystal composition, the optically-anisotropiclayer that is formed of the cured layer of the liquid crystalcomposition is obtained by immobilizing the predetermined liquid crystalalignment pattern can be obtained.

Next, each of the components of the liquid crystal composition accordingto the embodiment of the present invention will be described in detail.

The optically-anisotropic layer 14 is formed of a cured layer of aliquid crystal composition including a rod-shaped liquid crystalcompound or a disk-shaped liquid crystal compound, and has a liquidcrystal alignment pattern in which an optical axis of the rod-shapedliquid crystal compound or an optical axis of the disk-shaped liquidcrystal compound is aligned as described above.

By forming an alignment film on the support 12, applying the liquidcrystal composition to the alignment film, and curing the applied liquidcrystal composition, the optically-anisotropic layer consisting of thecured layer of the liquid crystal composition can be obtained. Althoughthe optically-anisotropic layer functions as a so-called λ/2 plate, thepresent invention also includes an aspect where a laminate including thesupport 12 and the alignment film that are integrated functions as aso-called λ/2 plate.

In addition, the liquid crystal composition for forming theoptically-anisotropic layer includes a rod-shaped liquid crystalcompound or a disk-shaped liquid crystal compound and may furtherinclude other components such as a leveling agent, an alignmentcontroller, a polymerization initiator, or an alignment assistant.

In addition, it is preferable that the optically-anisotropic layer has awide range for the wavelength of incidence light and is formed of aliquid crystal material having a reverse birefringence dispersion.

Further, it is also preferable that the optically-anisotropic layer canbe made to have a substantially wide range for the wavelength ofincidence light by imparting a torsion component to the liquid crystalcomposition or by laminating different phase difference layers. Forexample, in the optically-anisotropic layer, a method of realizing a λ/2plate having a wide-range pattern by laminating two liquid crystallayers having different twisted directions is disclosed in, for example,JP2014-089476A and can be preferably used in the present invention.

—Rod-Shaped Liquid Crystal Compound—

As the rod-shaped liquid crystal compound, an azomethine compound, anazoxy compound, a cyanobiphenyl compound, a cyanophenyl ester compound,a benzoate compound, a phenyl cyclohexanecarboxylate compound, acyanophenylcyclohexane compound, a cyano-substituted phenylpyrimidinecompound, an alkoxy-substituted phenylpyrimidine compound, aphenyldioxane compound, a tolan compound, or analkenylcyclohexylbenzonitrile compound is preferably used. As therod-shaped liquid crystal compound, not only the above-described lowmolecular weight liquid crystal molecules but also high molecular weightliquid crystal molecules can be used.

It is preferable that the alignment of the rod-shaped liquid crystalcompound is immobilized by polymerization. Examples of the polymerizablerod-shaped liquid crystal compound include compounds described inMakromol. Chem., (1989), Vol. 190, p. 2255, Advanced Materials (1993),Vol. 5, p. 107, U.S. Pat. Nos. 4,683,327A, 5,622,648A, 5,770,107A,WO95/022586A, WO95/024455A, WO97/000600A, WO98/023580A, WO98/052905A,JP1989-272551A (JP-H1-272551A), JP1994-016616A (JP-H6-016616A),JP1995-110469A (JP-H7-110469A), JP1999-080081A (JP-H 11-080081A), andJP2001-064627A. Further, as the rod-shaped liquid crystal compound, forexample, compounds described in JP1999-513019A (JP-H11-513019A) andJP2007-279688A can be preferably used.

—Disk-Shaped Liquid Crystal Compound—

As the disk-shaped liquid crystal compound, for example, compoundsdescribed in JP2007-108732A and JP2010-244038A can be preferably used.

In a case where the disk-shaped liquid crystal compound is used in theoptically-anisotropic layer, the liquid crystal compound 20 rises in thethickness direction in the optically-anisotropic layer, and the opticalaxis 22 derived from the liquid crystal compound is defined as an axisperpendicular to a disk surface, that is so-called, a fast axis.

The optically-anisotropic layer 14 can be formed by applying multiplelayers of the liquid crystal composition to the alignment film 13.

The application of the multiple layers refers to repetition of thefollowing processes including: preparing a first liquid crystalimmobilized layer by applying the liquid crystal composition to thealignment film, heating the liquid crystal composition, cooling theliquid crystal composition, and irradiating the liquid crystalcomposition with ultraviolet light for curing; and preparing a second orsubsequent liquid crystal immobilized layer by applying the liquidcrystal composition to the liquid crystal immobilized layer, heating theliquid crystal composition, cooling the liquid crystal composition, andirradiating the liquid crystal composition with ultraviolet light forcuring as described above. Even in a case where theoptically-anisotropic layer 14 is formed by the application of themultiple layers such that the total thickness of theoptically-anisotropic layer 14 is large, the alignment direction of thealignment film 13 can be reflected from a lower surface of theoptically-anisotropic layer 14 to an upper surface thereof

[Action of Collecting Lens]

As described above, in a preferable aspect, the light deflection device100 in the example shown in the drawing includes the collecting lens 131on the upstream side of the liquid crystal optical phase modulationelement 101.

The refraction of light from the optically-anisotropic layer 14 (liquidcrystal diffraction element 121) gradually increases from the centertoward the outside in the deflection direction.

On the other hand, light, that is, a light beam deflected from the lightdeflection device 100 is thick in practice. Therefore, to be exact, theamounts of refraction of light from the optically-anisotropic layer 14on the inside (the center side of deflection) and the outside in thedeflection direction are different from each other, and the amount ofrefraction on the outside is more than that on the inside. Therefore,the light refracted from the liquid crystal diffraction element 121increases in diameter so as to be slightly diffused.

On the other hand, by providing the collecting lens 131 such that thelight incident into the liquid crystal diffraction element 121 slightlydecreases in diameter, light emitted from the light deflection device100 (liquid crystal diffraction element 121) can be converted intoparallel light to improve straightness.

As a result, by providing the collecting lens 131, the scanning of lightusing the light deflection device 100 can be accurately performed evenin a case where an object to be scanned with light is distant from thelight deflection device 100.

The refractive power (lens power) of the collecting lens 131 is notlimited.

That is, the refractive power of the collecting lens 131 may beappropriately set to refractive power capable of emitting suitable lightbased on the amount of refraction from the liquid crystal diffractionelement 121 and the in-plane distribution thereof (that is, an in-planedistribution function of a diffraction pitch), the deflection angle oflight from the light deflection device 100, the distance between thelight deflection device 100 and the object to be scanned with light, thediameter of incidence light (beam diameter), and the like.

In addition, the position of the collecting lens 131 is not particularlylimited as long as it is present upstream of the liquid crystaldiffraction element 121. From the viewpoint that, for example, thecollecting lens 131 can be reduced and can be easily designed, it ispreferable that the collecting lens 131 is provided upstream of theliquid crystal optical phase modulation element 101 (light deflectionelement).

FIG. 10 is a schematic plan view showing an optically-anisotropic layerin a design modification example of the liquid crystal diffractionelement.

A liquid crystal alignment pattern in an optically-anisotropic layer 14Ashown in FIG. 10 is different from the liquid crystal alignment patternin the above-described optically-anisotropic layer 14. FIG. 10 showsonly the optical axis 22. The optically-anisotropic layer 14A in FIG. 10has the liquid crystal alignment pattern in which the direction of theoptical axis 22 gradually changes while rotating in multiple directionsfrom the center side toward the outside, for example along axes A₁, A₂,A₃, and . . . .

That is, the liquid crystal alignment pattern in theoptically-anisotropic layer 14A shown in FIG. 10 is a liquid crystalalignment pattern in which the optical axis 22 rotates radially. Inother words, the liquid crystal alignment pattern in theoptically-anisotropic layer 14A shown in FIG. 10 is a concentriccircular pattern having a concentric circular shape where the in-planedirection in which the direction of the optical axis changes whilecontinuously rotating moves from an inside toward an outside.

Depending on the liquid crystal alignment pattern shown in FIG. 10 , theabsolute phase of incidence light changes by different amounts of changebetween local regions having different directions of the optical axes22. In a case where the liquid crystal alignment pattern in which theoptical axis radially changes while rotating as shown in FIG. 10 isprovided, incidence light can be caused to transmit as diverging lightor collected light. That is, a function as a convex lens or a concavelens can be implemented by the liquid crystal alignment pattern in theoptically-anisotropic layer 14.

In a preferable aspect of the light deflection device according to theembodiment of the present invention, the liquid crystal diffractionelement 121 is used for the function of the concave lens of theoptically-anisotropic layer 14A shown in FIG. 10 . At this time, in acase where the center of the lens is matched to the center of emittedlight of the liquid crystal optical phase modulation element 101, themaximum deflection angle θmax of light emitted from the liquid crystaloptical phase modulation element can be extended most efficiently.

It is preferable that, as the size of divided regions (for example, 121a to 121 e) of the liquid crystal diffraction element 121 decreases, thechange is more smooth. The beam diameter of laser light to be emittedmay be a finite value to the extent that there is no problems inpractice. For example, the beam diameter may be 10 to several hundredsof micrometers.

In the light deflection device according to the embodiment of thepresent invention, by using the liquid crystal diffraction element 121Afor the function of the concave lens of the optically-anisotropic layer14A shown in FIG. 10 , light can be deflected so as to be radiallydiffused from the center.

For example, in the light deflection device according to the embodimentof the present invention, as conceptually shown in FIG. 16 , the liquidcrystal diffraction element 121A including the optically-anisotropiclayer 14A that functions as the concave lens, and, as the lightdeflection element, the light deflection element 101A that radiallydeflects light are used. The light deflection element 101A deflectslight, for example, at an orientation of 360° and a polar angle of 0° to35°.

As a result, as shown in FIG. 16 , the light L radially deflected fromthe light deflection element 101A is refracted from the liquid crystaldiffraction element 121A such that the deflection angle, that is, theazimuthal angle from the light deflection element 101A can be extended,and light can be deflected radially in a wide range. In addition, in apreferable aspect of the light deflection device according to theembodiment of the present invention, the collecting lens 131 isprovided. The light L is incident into the light deflection element 101Aas collected light and deflected by the collecting lens 131, and thecollected light is incident into the liquid crystal diffraction element121A as it is. As a result, the light refracted by the liquid crystaldiffraction element 121A is deflected and emitted as parallel light.

Examples of the light deflection element 101A that radially deflectslight include a well-known MEMS (Micro Electro Mechanical Systems) lightdeflection element (for example, a MEMS scanner (light scanner), a MEMSlight deflector, a MEMS mirror, or a digital micromirror device (DMD))that swings a mirror using a piezoelectric actuator to deflect light(deflection scanning), for example, a MEMS light deflection elementdescribed in JP2012-208352A, a MEMS light deflection element describedin JP2014-134642A, or a MEMS light deflection element described inJP2015-022064A.

In the above-described example, the liquid crystal compound 20 of theliquid crystal diffraction element faces one side in the thicknessdirection, but the present invention is not limited thereto.

In the light deflection device according to the embodiment of thepresent invention, the optically-anisotropic layer forming the liquidcrystal diffraction element may include the liquid crystal compound 20that is twisted and aligned along a helical axis extending in thethickness direction as in a first optically-anisotropic layer 215 and asecond optically-anisotropic layer 216 shown in FIG. 14 . In thefollowing description, the twisted alignment along the helical axisextending in the thickness direction will also simply referred to as“twisted alignment”.

The first optically-anisotropic layer 215 and the secondoptically-anisotropic layer 216 in which the liquid crystal compound 20is twisted and aligned are tilted optically-anisotropic layers in which,in a cross-sectional SEM image obtained by observing a cross-section ofthe liquid crystal diffraction element 220 with a scanning electronmicroscope (SEM), bright and dark lines derived from the twistedalignment of the liquid crystal compound 20 are tilted with respect tothe normal line of an interface between the first optically-anisotropiclayer 215 and the second optically-anisotropic layer 216 as shown inFIG. 14 .

As described above, in the liquid crystal alignment pattern, in a casewhere the single period (rotation period p) over which the optical axisof the liquid crystal compound rotates by 180° gradually decreases inthe direction in which the optical axis 22 rotates, the tilt angle ofthe bright and dark lines with respect to the normal line of the firstoptically-anisotropic layer 215 and the second optically-anisotropiclayer 216 gradually decreases in the direction in which the optical axis22 rotates. That is, in this case, the tilt angle of the bright and darklines rises with respect to the main surface of theoptically-anisotropic layer. Further, in this case, in the pattern ofthe bright and dark lines of the first optically-anisotropic layer 215and the second optically-anisotropic layer 216, the period decreases inthe direction in which the optical axis 22 rotates.

This way, in the optically-anisotropic layer including the twisted andaligned liquid crystal compound 20, the diffraction efficiency of lightcan be improved even by high-angle diffraction. As a result, as comparedto the optically-anisotropic layer shown in FIG. 5 in which the liquidcrystal compound is not twisted and aligned, a decrease in light amountin the optically-anisotropic layer can be suppressed, and the amount ofemitted light can be improved.

In the liquid crystal diffraction element 220, the twisted direction inthe twisted alignment of the liquid crystal compound 20 in the firstoptically-anisotropic layer 215 is different from that in the secondoptically-anisotropic layer 216. That is, in the firstoptically-anisotropic layer 215, the liquid crystal compound 20 istwisted and aligned clockwise in the light traveling direction. That is,in the second optically-anisotropic layer 216, the liquid crystalcompound 20 is twisted and aligned counterclockwise in the lighttraveling direction.

Therefore, the direction of tilt of the bright and dark lines derivedfrom the twisted alignment in the cross-sectional SEM image of the firstoptically-anisotropic layer 215 is different from that in the secondoptically-anisotropic layer 216.

In the first optically-anisotropic layer 215, for example, in a casewhere incidence light is right circularly polarized light, the effect ofimproving the diffraction efficiency is high for light that travels tothe left side (outside) indicated by a solid line in the drawing.However, in the first optically-anisotropic layer 215, for example, in acase where incidence light is right circularly polarized light, theeffect of improving the diffraction efficiency is low for light thattravels to the right side (center side) indicated by a broken line inthe drawing.

On the other hand, in the second optically-anisotropic layer 216, forexample, in a case where incidence light is right circularly polarizedlight, conversely, the effect of improving the diffraction efficiency islow for light that travels to the left side (outside) indicated by asolid line in the drawing. However, in the second optically-anisotropiclayer 216, in a case where incidence light is right circularly polarizedlight, the effect of improving the diffraction efficiency is high forlight that travels to the right side (center side) indicated by a brokenline in the drawing.

The effects are opposite in a case where incidence light is leftcircularly polarized light.

In the liquid crystal diffraction element 220, only the light thattravels to the left side (outside) indicated by the solid line in thedrawing is incident into a region in FIG. 14 where the center ofdeflection is on the right side in the drawing. Accordingly, for thelight (right circularly polarized light), that is, in the region on theleft side from the center in the drawing, the firstoptically-anisotropic layer 215 acts strongly, the diffractionefficiency is improved, and the amount of emitted light can beincreased.

On the other hand, only the right that travels to the right sideindicated by the broken line in the drawing is incident into the regionon the right side from the center in FIG. 14 . Accordingly, for thelight (right circularly polarized light), the secondoptically-anisotropic layer 216 acts strongly, the diffractionefficiency is improved, and the amount of emitted light can beincreased.

In addition, in the region at the center of polarization, the incidenceangle of incidence light into the optically-anisotropic layer is small.Both the first optically-anisotropic layer 215 and the secondoptically-anisotropic layer 216 contribute to the improvement of thediffraction efficiency.

As a result, in the liquid crystal diffraction element 220 including thefirst optically-anisotropic layer 215 and the secondoptically-anisotropic layer 216 that have different twisted directionsin the twisted alignment of the liquid crystal compound 20, the effectof improving the diffraction efficiency can be improved over the entireregion in the light deflection direction, and a large amount of lightcan be emitted in the entire range of the deflection angle.

In the optically-anisotropic layer in which the liquid crystal compound20 is twisted and aligned, the twisted angle of the liquid crystalcompound is not limited. The twisted angle of liquid crystal compoundmay be appropriately set according to the deflection angle from thelight deflection element, the desired diffraction efficiency, and thelike.

In the optically-anisotropic layer in which the liquid crystal compound20 is twisted and aligned, the twisted angle of the liquid crystalcompound 20 is preferably 10° to 200°, more preferably 20° to 190°, andstill more preferably 40° to 170°.

The twisted angle of the twisted and aligned liquid crystal compound 20(the twisted angle in the thickness direction) refers to a twisted anglefrom a lower surface to an upper surface of the liquid crystal compound20 that is twisted and aligned along the helical axis extending in thethickness direction in the optically-anisotropic layer.

This way, in the liquid crystal diffraction element including the firstoptically-anisotropic layer 215 and the second optically-anisotropiclayer 216 in which the liquid crystal compound 20 is helically twistedand aligned, a third optically-anisotropic layer 219 in which the liquidcrystal compound 20 is not twisted and aligned may be provided betweenthe first optically-anisotropic layer 215 and the secondoptically-anisotropic layer 216 as in a liquid crystal diffractionelement 224 shown in FIG. 15 .

The third optically-anisotropic layer 219 in which the liquid crystalcompound is not twisted and aligned is a non-tiltedoptically-anisotropic layer in which bright and dark lines extend in thenormal direction.

By providing the third optically-anisotropic layer 219 between the firstoptically-anisotropic layer 215 and the second optically-anisotropiclayer 216, light can be deflected at a wider deflection angle due to thesynergistic effect of diffraction from the third optically-anisotropiclayer 219.

In the above description, the liquid crystal diffraction element 121 isused as a transmission diffraction element. However, in the lightdeflection device according to the embodiment of the present invention,a reflective liquid crystal diffraction element can also be used.

In this case, the same forming method can be adopted, except that theliquid crystal compositions are different from each other. By using acholesteric liquid crystal as liquid crystal and using the samealignment film as that of the transmission diffraction element,reflective diffracted light can be generated, and the angle can beextended. As a light reflection element that reflects light in adirection different from the incidence angle, a micromirror or amicrolens that collects or diffuses light or a light collecting mirrorfor a sensor can be used.

In the light deflection device according to the embodiment of thepresent invention, the light deflection element is not limited to theliquid crystal optical phase modulation element 101, and well-knownvarious light deflection elements such as a galvanometer mirror, apolygon mirror, a MEMS light deflection element can be used.

In particular, from the viewpoint that the size of a mechanical movableportion and the number of mechanical movable portions are small, theabove-described liquid crystal optical phase modulation element 101 andthe MEMS light deflection element can be suitably used as the lightdeflection element.

FIG. 13 conceptually shows an example of the light deflection deviceaccording to the embodiment of the present invention including the MEMSlight deflection element.

In a light deflection device 130 shown in FIG. 13 , a large number ofmembers that are the same as those of the light deflection device 100are used. Therefore, the same members are represented by the samereference numerals, and different members will be mainly describedbelow.

In the light deflection device 130 shown in FIG. 13 , P polarized lightemitted from a light source (not shown) with respect to the emissionsurface 161 of the liquid crystal diffraction element 121 is slightlycollected by the collecting lens 131 and is converted into, for example,right circularly polarized light by the λ/4 plate 111.

In the light deflection device 130 including the MEMS light deflectionelement 132, the λ/4 plate 111 may be disposed between the MEMS lightdeflection element 132 and the liquid crystal diffraction element 121 asin the light deflection device 100 shown in FIG. 1 . However, forexample, from the viewpoint that the λ/4 plate 111 can be reduced, inthe light deflection device 130 including the MEMS light deflectionelement 132, it is preferable that the λ/4 plate 111 is providedupstream of the MEMS light deflection element 132.

In addition, in the light deflection device 130 including the MEMS lightdeflection element 132, in a case where circularly polarized light isincident the λ/4 plate 111 is not necessarily provided.

In the light deflection device 130, it is preferable that the mirror ofthe MEMS light deflection element 132 is not depolarized. Specifically,for example, a metal mirror having a mirror surface is used. In themetal mirror, in a case where circularly polarized light is reflected,the twisting (sense) of circularly polarized light is reversed.Therefore, in order to twist circularly polarized light in a desireddirection during incidence into the liquid crystal diffraction element,it is preferable that circularly polarized light having an oppositetwisted direction is incident into the MEMS light polarization element.

In a case where the incidence angle is large with respect to the mirrorsurface of the MEMS light deflection element 132, the polarization stateof light changes because P polarized light (P wave) and S polarizedlight (S wave) have different reflectivities and different phases.Accordingly, the polarization state may be adjusted in advance such thatdesired circularly polarized light can be obtained after being reflectedfrom the mirror. Examples of a method of adjusting the polarizationstate include a method of using elliptically polarized light. Inaddition, a phase difference plate for adjusting the phase may bedisposed such that desired circularly polarized light can be obtainedafter being reflected from the mirror of the MEMS light deflectionelement 132.

Further, a circularly polarized light mirror, for example, a cholestericliquid crystal layer may be used as the mirror of the MEMS lightdeflection element 132. In a circularly polarized light mirror, forexample, a cholesteric liquid crystal layer, the twisted direction ofcircularly polarized light is maintained during reflection. Therefore,in order to twist circularly polarized light in a desired directionduring incidence into the liquid crystal diffraction element 121, it ispreferable that circularly polarized light having the same twisteddirection is incident into the MEMS light polarization element 132.

Light that is converted into circularly polarized light by the λ/4 plate111 is deflected from the MEMS light deflection element 132. Thedeflection direction of light from the MEMS light deflection element 132matches the axis A direction (arrow X direction) as in theabove-described light deflection device 100.

In FIG. 13 , reference numeral 134 represents a drive unit of the MEMSlight deflection element 132. As the drive unit 134, a well-known unitcorresponding to the configuration of the MEMS light deflection element132 and the like may be used.

In the light deflection device 130 according to the embodiment of thepresent invention, the MEMS light deflection element 132 is notparticularly limited, and a well-known MEMS (Micro Electro MechanicalSystems) light deflection element (for example, a MEMS scanner (lightscanner), a MEMS light deflector, a MEMS mirror, or a DMD) that swings amirror using a piezoelectric actuator to deflect light (deflectionscanning), for example, a MEMS light deflection element described inJP2012-208352A, a MEMS light deflection element described inJP2014-134642A, or a MEMS light deflection element described inJP2015-022064A can be used.

The light deflected from the MEMS light deflection element 132 isdiffracted from the liquid crystal diffraction element 121 as in thelight deflection device 100, the deflection angle is extended asdescribed above, and the diffracted light is emitted from the lightdeflection device 130 at the desired maximum emission angle θmaxout thatis more than the maximum deflection angle θmax of the MEMS lightdeflection element 132.

In the above description, in a preferable aspect of the light deflectiondevice according to the embodiment of the present invention, the liquidcrystal diffraction element 121 including the optically-anisotropiclayer 14 having the liquid crystal alignment pattern in which adirection of an optical axis derived from the liquid crystal compoundchanges while continuously rotating in at least one in-plane directionis used as a diffraction element, but the present invention is notlimited thereto.

That is, in the light deflection device according to the embodiment ofthe present invention, all the well-known diffraction elements can beused as long as the periodic structure pitch gradually changes such thatthe diffraction angle increases from the center of deflection from thelight deflection element toward the outside.

In a preferable example, a method of using photonic crystal withoutusing a liquid crystal material can also be used with the same principleas that of the above-described liquid crystal diffraction element.

For example, as in a method described in JP2017-111277A, a transparentsubstrate that is formed of an inorganic material and an uneven patternforming portion that is formed of a plurality of protrusions formed ofSi or the like are provided at a regular interval such that structuralbirefringence occurs and the azimuthal angle is changed in a plane. As aresult, the same diffraction effect as that of the above-describedliquid crystal alignment pattern can be obtained.

Examples of another preferable diffraction element include a hologramdiffraction element that exposes a photosensitive material or the liketo a pattern shape by holography and diffracts light according to adifference in the refractive index of the exposed portion.

The hologram diffraction element may have a periodic refractive indexdistribution that gradually changes from the center of deflection fromthe light deflection element toward both end portions such that thediffraction angle increases, for example, from the center of deflectionfrom the light deflection element toward the outside.

The hologram diffraction element is not particularly limited as long asthe above-described requirements are satisfied. For example, awell-known hologram diffraction element (holographic diffraction element(diffraction grating)) such as a hologram sheet described inJP2016-184124A or can be used.

As still another preferable diffraction element, a surface reliefdiffraction element that diffracts light with a fine uneven portionformed on the surface can also be used.

In the surface relief diffraction element, an uneven grating period(relief pattern) gradually changes from the center of deflection fromthe light deflection element toward both end portions such that thediffraction angle increases, for example, from the center of deflectionfrom the light deflection element toward both end portions.

The surface relief diffraction element is not particularly limited aslong as the above-described requirements are satisfied. For example, allthe well-known surface relief diffraction elements such as a structuredescribed in JP2015-093439A can be used.

In a case where the hologram diffraction element or the surface reliefdiffraction element is used as the diffraction element, light incidentinto the diffraction element is not necessarily circularly polarizedlight. Accordingly, in this case, the λ/4 plate 111 is unnecessary.

As can be seen from the above description, the light deflection deviceaccording to the embodiment of the present invention can realize a lightand small light deflection device that has a simple structure, can beeasily driven, has no mechanical movable portion, and thus is suitablefor free-space optical communication, a laser radar, or an light scannerwhere light can be deflected at a large angle.

The light deflection device according to the embodiment of the presentinvention can realize a high-performance light deflection device havinga simple configuration using a simple driving method.

The light deflection device according to the embodiment of the presentinvention can be used in various optical devices.

FIG. 17 conceptually shows an example of an optical device according tothe embodiment of the present invention including the light deflectiondevice according to the embodiment of the present invention.

An optical device 110 shown in FIG. 17 includes a light source 112, thelight deflection device 100 according to the embodiment of the presentinvention, and a light-receiving element 114.

In the optical device 110, light emitted from the light source 112 isdeflected from the light deflection device 100 according to theembodiment of the present invention. The deflected light is emitted fromthe optical device 110 and reflected from a measurement target O. Thereflected light from the measurement target O is incident again into theoptical device 110, is received by the light-receiving element 114, andis measured.

The optical device 110 according to the embodiment of the presentinvention is used as various sensors. Examples of the sensors using theoptical device 110 include a distance-measuring sensor using lightdetection and ranging (LiDAR), a shape-measuring sensor, and arecognition sensor.

In the optical device 110, the light source 112 is not particularlylimited, and an appropriate light source may be selected depending onthe measurement target, the use of the optical device 110, and the like.Examples of the light source 112 include a semiconductor laser, a laserdiode (LD), and a light emitting diode (LED). For example, in a casewhere the optical device 110 is used as a distance-measuring sensor, forexample, a light source that emits infrared light is preferably used asthe light source 112. In addition, depending on targets to be measuredand environments, for example, a light source that emits light having awavelength other than infrared light or an electromagnetic wave can alsobe preferably used. For example, a laser light source that emits visiblelight may be used as the light source 112.

The light-receiving element 114 is not particularly limited, and variouswell-known light-receiving elements can be used as long as they canmeasure light emitted from the light source 112. Examples of thelight-receiving element 114 include a charge coupled device (CCD) sensorand a photomultiplier.

In addition, the light deflection device according to the embodiment ofthe present invention has a simple structure, can be easily driven, andcan deflect light at a large angle. Therefore, the light deflectiondevice according to the embodiment of the present invention can be usedfor various uses where a reduction in weight and size is desired andlight is scanned.

Examples of the uses of the light deflection device according to theembodiment of the present invention include a drawing device using beamscanning, a beam scanning projection display, a beam scanning head-updisplay, and beam scanning AR glasses. In this case, the lightdeflection device according to the embodiment of the present inventioncan be used as a device that deflects light in a wide wavelength rangeincluding visible light.

EXAMPLES

Hereinafter, the characteristics of the present invention will bedescribed in detail using examples. Materials, chemicals, used amounts,material amounts, ratios, treatment details, treatment procedures, andthe like shown in the following examples can be appropriately changedwithin a range not departing from the scope of the present invention.Accordingly, the scope of the present invention is not limited to thefollowing specific examples.

Example 1

<Preparation of Liquid Crystal Optical Phase Modulation Element>

As the liquid crystal optical phase modulation element, an elementdescribed in JP2003-295153A was used.

That is, in the liquid crystal optical phase modulation element anematic liquid crystal layer is provided between a transparent substrateincluding a plurality of individual ITO electrodes arranged in aparallel stripe shape and a transparent substrate including a common ITOelectrode formed of a transparent conductor. By applying a predeterminedvoltage to each of the individual electrodes, the modulation of therefractive index occurred in the nematic liquid crystal layer.

As a result, it was verified that infrared laser light (wavelength: 940nm; linearly polarized light; the orientation of the polarizing axis wasextraordinary light orientation of liquid crystal) was bent to anorientation perpendicular to the orientation of the parallel stripebelt. The deflection angle was about ±3°.

<Preparation of Liquid Crystal Diffraction Element>

(Support and Saponification Treatment of Support)

As the support, a commercially available triacetyl cellulose film(manufactured by Fuji Film Co., Ltd., Z-TAC) was used.

The support was caused to pass through an induction heating roll at atemperature of 60° C. such that the support surface temperature wasincreased to 40° C.

Next, an alkali solution shown below was applied to a single surface ofthe support using a bar coater in an application amount of 14 mL(liter)/m², the support was heated to 110° C., and the support wastransported for 10 seconds under a steam infrared electric heater(manufactured by Noritake Co., Ltd.).

Next, 3 mL/m² of pure water was applied to a surface of the support towhich the alkali solution was applied using the same bar coater. Next,water cleaning using a foundry coater and water draining using an airknife were repeated three times, and then the support was transportedand dried in a drying zone at 70° C. for 10 seconds. As a result, thealkali saponification treatment was performed on the surface of thesupport.

Alkali Solution

Potassium hydroxide 4.70 parts by mass Water 15.80 parts by massIsopropanol 63.70 parts by mass Surfactant SF-1: C₁₄H₂₉O(CH₂CH₂O)2OH 1.0part by mass Propylene glycol 14.8 parts by mass

(Formation of Undercoat Layer)

The following undercoat layer-forming coating solution was continuouslyapplied to the surface of the support on which the alkali saponificationtreatment was performed using a #8 wire bar. The support on which thecoating film was formed was dried using warm air at 60° C. for 60seconds and was dried using warm air at 100° C. for 120 seconds. As aresult, an undercoat layer was formed.

Undercoat Layer-Forming Coating Solution

The following modified polyvinyl alcohol 2.40 parts by mass Isopropylalcohol 1.60 parts by mass Methanol 36.00 parts by mass Water 60.00parts by mass Modified Polyvinyl Alcohol

(Formation of Alignment Film)

The following alignment film-forming coating solution was continuouslyapplied to the support on which the undercoat layer was formed using a#2 wire bar. The support on which the coating film of the alignmentfilm-forming coating solution was formed was dried using a hot plate at60° C. for 60 seconds. As a result, an alignment film was formed.

Alignment Film-Forming Coating Solution

Material A for photo-alignment 1.00 part by mass Water 16.00 parts bymass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether42.00 parts by mass Material A for Photo-Alignment

(Exposure of Alignment Film)

The alignment film was exposed using the exposure device shown in FIG.12 to form an alignment film P-1 having an alignment pattern.

In the exposure device, a laser that emits laser light having awavelength (405 nm) was used as the laser. The exposure dose of theinterference light was 100 mJ/cm².

By adjusting the refractive power of the lens (convex lens), during thesubsequent formation of the optically-anisotropic layer, the rotationperiod of the optical axis of the liquid crystal compound in theoptically-anisotropic layer gradually decreased from the center towardthe outside.

(Formation of Optically-Anisotropic Layer)

As the liquid crystal composition forming the optically-anisotropiclayer, the following composition A-1 was prepared.

Composition A-1

Liquid crystal compound L-1 100.00 parts by mass Polymerizationinitiator (IRGACURE (registered trade name) 907, manufactured by BASFSE) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, manufactured byNippon Kayaku Co., Ltd.) 1.00 part by mass Leveling agent T-1 0.08 partsby mass Methyl ethyl ketone 313.00 parts by mass Liquid Crystal CompoundL-1

Leveling Agent T-1

The optically-anisotropic layer was formed by applying multiple layersof the composition A-1 to the alignment film P-1. The application of themultiple layers refers to repetition of the following processesincluding: preparing a first liquid crystal immobilized layer byapplying the first layer-forming composition A-1 to the alignment film,heating the composition A-1, cooling the composition A-1, andirradiating the composition A-1 with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition A-1 to theformed liquid crystal immobilized layer, heating the composition A-1,cooling the composition A-1, and irradiating the composition A-1 withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the liquid crystal layer waslarge, the alignment direction of the alignment film was reflected froma lower surface of the liquid crystal layer to an upper surface thereof.

Regarding the first liquid crystal layer, the composition A-1 wasapplied to the alignment film P-1 to form a coating film, the coatingfilm was heated using a hot plate at 70° C., the coating film was cooledto 25° C., and the coating film was irradiated with ultraviolet lighthaving a wavelength of 365 nm at an irradiation dose of 100 mJ/cm² usinga high-pressure mercury lamp in a nitrogen atmosphere. As a result, thealignment of the liquid crystal compound was immobilized. At this time,the thickness of the first liquid crystal layer was 0.2 μm.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the first liquid crystal layer, and the appliedcomposition was heated, cooled, and irradiated with ultraviolet lightfor curing under the same conditions as described above. As a result, aliquid crystal immobilized layer was prepared. This way, by repeatingthe application multiple times until the total thickness reached adesired thickness, an optically-anisotropic layer was obtained. As aresult, a liquid crystal diffraction element including the support, thealignment film, and the optically-anisotropic layer was prepared.

In the optically-anisotropic layer, finally, Δn₉₄₀×Thickness (Re(940))of the liquid crystal was 470 nm, and a periodic liquid crystalalignment pattern having a concentric circular shape as shown in FIG. 10was provided. Further it was verified with a polarizing microscope thatthe rotation period of the optical axis of the liquid crystal compoundin the optically-anisotropic layer gradually decreased from the centertoward the outside in the in-plane direction in which the optical axisrotated and that the rotation direction of the optical axis was reversedat the center.

In the liquid crystal alignment pattern of the optically-anisotropiclayer, regarding the rotation period (single period) over which theoptical axis of the liquid crystal compound rotated by 180°, therotation period of a center portion was significantly large (the inverseof the rotation period was 0), the rotation period of a portion at adistance of 2.5 mm from the center was 10.6 μm, and the rotation periodof a portion at a distance of 5.0 mm from the center was 5.3 μm. Thisway, the rotation period gradually decreased from the center toward theouter direction.

<Preparation of λ/4 Plate>

In order to convert linearly polarized light transmitted through theliquid crystal optical phase modulation element into circularlypolarized light and to be incident into the liquid crystal diffractionelement, a λ/4 plate (circular polarization plate) was prepared.

First, the support on which the undercoat layer was formed as describedabove was prepared.

(Formation of Alignment Film P-10)

The following alignment film P-10-forming coating solution wascontinuously applied to the support on which the undercoat layer wasformed using a #2.4 wire bar. The support on which the coating film ofthe alignment film P-10-forming coating solution was formed was driedusing a hot plate at 80° C. for 5 minutes. As a result, an alignmentfilm P-10 was formed.

<Alignment Film P-10-Forming Coating Solution>

Material for photo-alignment Polymer A2 4.35 parts by mass Low molecularweight compound B2 0.80 parts by mass Crosslinking agent C1 2.20 partsby mass Compound D1 0.48 parts by mass Compound D2 1.15 parts by massButyl acetate 100.00 parts by mass

<<Synthesis of Polymer A2>>

100 parts by mass of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 500parts by mass of methyl isobutyl ketone, and 10 parts by mass oftriethylamine were charged into a reaction vessel equipped with astirrer, a thermometer, a dropping funnel, and a reflux cooling pipe andwere mixed with each other at room temperature. Next, 100 parts by massof deionized water was dropped for 30 minutes using a dropping funnel,and a reaction was caused to occur at 80° C. for 6 hours while mixingthe components with each other under reflux. After completion of thereaction, the organic phase was extracted and was cleaned with 0.2 mass% ammonium nitrate aqueous solution until water used for cleaning wasneutral. Next, by distilling off the solvent and water under reducedpressure, epoxy-containing polyorganosiloxane was obtained as a viscoustransparent liquid

In a case where the epoxy-containing polyorganosiloxane was analyzed bynuclear magnetic resonance (¹H-NMR), a peak having a theoreticalintensity based on an oxiranyl group was obtained in the vicinity ofchemical shift (δ)=3.2 ppm, and it was verified that a side reaction ofan epoxy group did not occur during the reaction. In theepoxy-containing polyorganosiloxane, the weight-average molecular weightMw was 2,200, and the epoxy equivalent was 186 g/mol.

Next, 10.1 parts by mass of the epoxy-containing polyorganosiloxaneobtained as described above, 0.5 parts by mass of an acrylicgroup-containing carboxylic acid (manufactured by Toagosei Co., Ltd.,ARONIX M-5300, ω-carboxypolycaprolactone monoacrylate (polymerizationdegree n≈2)), 20 parts by mass of butyl acetate, 1.5 parts by mass of acinnamic acid derivative obtained using a method of Synthesis Example 1of JP2015-026050A, and 0.3 parts by mass of tetrabutylammonium bromidewere charged into a 100 mL three-neck flask, and were stirred at 90° C.for 12 hours. After completion of the reaction solution was diluted withthe same amount (mass) of butyl acetate as that of the reaction solutionand was cleaned with water three times.

An operation of concentrating this solution and diluting theconcentrated solution with butyl acetate was repeated twice. Finally, asolution including polyorganosiloxane (the following polymer A2) havinga photo-alignable group was obtained. In the polymer A2, theweight-average molecular weight Mw was 9,000. In addition, as a resultof ¹H-NMR, the content of a component having a cinnamate group in thepolymer A2 was 23.7 mass %.

—Polymer A2—

—Low Molecular Weight Compound B2—

The low molecular weight compound B2 shown in the following table(manufactured by Nissin Ion Equipment Co., Ltd., NOMCOAT TAB) was used.

—Crosslinking Agent C1—

The crosslinking agent C1 (manufactured by Nagase ChemteX Corporation,DENACOL EX411) shown in the following table was used.

—Compound D1—

The following compound D1 (manufactured by Kawaken Fine Chemicals Co.,Ltd., ALUMINUM CHELATE A(W)) shown in the following table was used.

—Compound D2—

The compound D2 (manufactured by Toyo Science Corp., triphenylsilanol)shown in the following table was used.

(Exposure of Alignment Film P-10)

By irradiating the obtained alignment film P-10 with polarizedultraviolet light (20 mJ/cm², using an extra high pressure mercurylamp), the alignment film P-10 was exposed.

[Preparation of λ/4 Plate]

The optically-anisotropic layer was formed by applying the compositionA-1 to the alignment film P-10.

The applied coating film was heated using a hot plate at 110° C., thecoating film was cooled to 60° C., and the coating film was irradiatedwith ultraviolet light having a wavelength of 365 nm at an irradiationdose of 500 mJ/cm² using a high-pressure mercury lamp in a nitrogenatmosphere. As a result, the alignment of the liquid crystal compoundwas immobilized, and an optically-anisotropic layer was prepared.Finally, the optically-anisotropic layer was transferred from thesupport to a quartz substrate having a thickness of 10 mm using anadhesive material. As a result, the λ/4 plate was obtained. In theobtained λ/4 plate, Δn₉₄₀×d (Re(940)) was 470 nm.

<Assembly of Light Deflection Device>

The liquid crystal optical phase modulation element, the λ/4 plate, andthe liquid crystal diffraction element were laminated in this order andwere bonded to each other using an adhesive material. As a result, alight deflection device shown in FIG. 1 was prepared. In addition, adrive unit was connected to the liquid crystal optical phase modulationelement.

At this time, the deflection orientation of emitted light of the liquidcrystal optical phase modulation element and the in-plane slow axis ofthe λ/4 plate were disposed to intersect at 45° such that the light wasconverted into circularly polarized light. In addition, the center ofthe deflection orientation of the liquid crystal optical phasemodulation element and the center of the liquid crystal diffractionelement were matched to each other, and the elements were bonded to eachother such that the amplification effect of the deflection angle oflight was able to be maximized.

In addition, as a light source, an infrared laser (wavelength: 940 nm;linearly polarized light; the orientation of the polarizing axis wasextraordinary light orientation of liquid crystal) was prepared. Theinfrared laser was disposed such that linearly polarized light to beemitted was P polarized light with respect to the emission surface ofthe liquid crystal diffraction element.

[Evaluation]

In the light deflection device according to Example 1, the infraredlaser light was incident from the front of the liquid crystal opticalphase modulation element in the light deflection device, a predeterminedvoltage was applied to the individual electrodes such that the liquidcrystal optical phase modulation element was changed at an angle of ±3°,and the angle of emitted light from the liquid crystal diffractionelement was measured.

As a result, it was able to be verified that the deflection angle(amount of deflection angle) from the liquid crystal optical phasemodulation element was largely extended by the liquid crystaldiffraction element by about ±55°.

In addition, a collecting lens (convex lens) was disposed between theinfrared laser and the liquid crystal optical phase modulation elementin the light deflection device, and the same evaluation was performed.As a result, it was able to be verified that the straightness of lightdeflected from the light deflection device was improved.

Example 2

A light deflection device having the configuration shown in FIG. 13 wasprepared by using the micromirror device described in JP2014-134642A asthe light deflection element instead of the liquid crystal optical phasemodulation element, and the same evaluation was performed.

In this example, the liquid crystal diffraction element was also changedto the following element. A method of preparing the liquid crystaldiffraction element was as follows.

<Preparation of Liquid Crystal Diffraction Element>

0.09 parts by mass of the following chiral agent was added to theabove-described composition A-1 to prepare a composition. Anoptically-anisotropic layer was formed using the same method asdescribed above, except that the composition was used. Δn₉₄₀×thickness(Re(940)) was 470 nm, and the twisted angle was 75° of the righttwisting.

Next, 0.09 parts by mass of the following chiral agent was added to theabove-described composition A-1 to prepare a composition. The secondoptically-anisotropic layer was formed on the previously formedoptically-anisotropic layer using the same method as described above,except that the composition was used. Δn₉₄₀×thickness (Re(940)) was 470nm, and the twisted angle was 75° of the left twisting.

As a result, a liquid crystal diffraction element in which two layerswere laminated was prepared, the two layers having a structure in whichthe liquid crystal compound was twisted and aligned and the twisteddirections were different from each other as shown in FIG. 14 . Thereason why the layers having different twisted directions were laminatedwas to obtain a high diffraction efficiency even by high-anglediffraction as described above.

The characteristic values of each of the other optical components shownin FIG. 13 are as described below.

The diameter of the laser light was 3 mm, the focal length of thecollecting lens was 35 mm, the distance between the collecting lens andthe micromirror device was 16 mm, and the distance between themicromirror device and the liquid crystal diffraction element was 7 mm.

The deflection angle of emitted light from the micromirror device was±35°. The diameter of the liquid crystal diffraction element was 20 mm.In the liquid crystal alignment pattern of the liquid crystaldiffraction element, the rotation period of a center portion wassignificantly large (the inverse of the rotation period was 0), therotation period at a position of a radius of 5 mm was 4.8 μm, and therotation period at a position of a radius of 10 mm was 2.6 μm. This way,the rotation period gradually decreased from the center toward the outerdirection.

Regarding the light deflection device according to Example 2, the angleof emitted light from the liquid crystal diffraction element wasmeasured and evaluated using the same method as that of Example 1.

In the evaluation, likewise, it was verified that the deflection anglefrom the micromirror device was largely extended by the liquid crystaldiffraction element, and the light was emitted at a deflection angle ofabout +70°.

Further, two light deflection devices including a liquid crystaldiffraction element different from that of the above-described examplewere prepared.

Example 3

<Preparation of Liquid Crystal Diffraction Element>

As conceptually shown in FIG. 14 , a liquid crystal diffraction elementincluding two optically-anisotropic layers of a firstoptically-anisotropic layer and a second optically-anisotropic layer wasprepared.

The first optically-anisotropic layer and the secondoptically-anisotropic layer are layers where the liquid crystal compoundis twisted and aligned, and are tilted optically-anisotropic layers inwhich, in a cross-sectional SEM image obtained by observing across-section of the liquid crystal diffraction element with a SEM,bright and dark lines derived from the twisted alignment of the liquidcrystal compound were tilted with respect to the normal line of aninterface between the first optically-anisotropic layer and the secondoptically-anisotropic layer as shown in FIG. 14 .

Further, the twisted direction in the twisted alignment of the liquidcrystal compound of the first optically-anisotropic layer was differentfrom that of the second optically-anisotropic layer. As a result, thetilt directions of the bright and dark lines derived from the twistedalignment in the cross-sectional SEM images were different from eachother.

In the following description, “the bright and dark lines derived fromthe twisted alignment” will also be simply referred to as “bright anddark lines”. In addition, “the normal line of the interface between thefirst optically-anisotropic layer and the second optically-anisotropiclayer” will also be simply referred to as “normal line”.

(Formation of First Optically-Anisotropic Layer)

As the liquid crystal composition forming the firstoptically-anisotropic layer, the following composition A-5 was prepared.

Composition A-5

Liquid crystal compound L-1 100.00 parts by mass Chiral agent A 0.13parts by mass Polymerization initiator (IRGACURE (registered trade name)907, manufactured by BASF SE) 3.00 parts by mass Photosensitizer(KAYACURE DETX-S, manufactured by Nippon Kayaku Co., Ltd.) 1.00 part bymass Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2840.00parts by mass Chiral Agent A

A first optically-anisotropic layer was formed on the alignment film P-1using the same method as that of the optically-anisotropic layeraccording to Example 1, except that the composition A-5 was used.

(Formation of Second Optically-Anisotropic Layer)

As the liquid crystal composition forming the secondoptically-anisotropic layer, the following composition A-6 was prepared.

Composition A-6

Liquid crystal compound L-1 100.00 parts by mass Chiral agent B 0.22parts by mass Polymerization initiator (IRGACURE (registered trade name)907, manufactured by BASF SE) 3.00 parts by mass Photosensitizer(KAYACURE DETX-S, manufactured by Nippon Kayaku Co., Ltd.) 1.00 part bymass Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2840.00parts by mass Chiral Agent B

A second optically-anisotropic layer was formed on the firstoptically-anisotropic layer 1 using the same method as that of theoptically-anisotropic layer according to Example 1, except that thecomposition A-6 was used. As a result, a liquid crystal diffractionelement including two optically-anisotropic layers as shown in FIG. 14was prepared.

In the first optically-anisotropic layer and the secondoptically-anisotropic layer of the prepared liquid crystal diffractionelement, finally, Δn₉₄₀×Thickness (=Re(940)) of the liquid crystal was470 nm, and a periodic liquid crystal alignment pattern having aconcentric circular shape as shown in FIG. 10 was provided. Further itwas verified with a polarizing microscope that the rotation period ofthe optical axis of the liquid crystal compound gradually decreased fromthe center toward the outside in the in-plane direction in which theoptical axis rotated and that the rotation direction of the optical axiswas reversed at the center.

In the liquid crystal alignment pattern of the firstoptically-anisotropic layer, regarding the rotation period (singleperiod) over which the optical axis of the liquid crystal compoundrotated by 180°, the rotation period of a center portion wassignificantly large (the inverse of the rotation period was considered0), the rotation period of a portion at a distance of 1.0 mm from thecenter was 9.0 μm, the rotation period of a portion at a distance of 2.5mm from the center was 4.5 μm, and the rotation period of a portion at adistance of 4.0 mm from the center was 3.0 μm. This way, the rotationperiod gradually decreased from the center toward the outer direction.

Further, the twisted direction in the liquid crystal compound of thefirst optically-anisotropic layer was opposite to that of the secondoptically-anisotropic layer. The twisted angle of the firstoptically-anisotropic layer in the thickness direction was 80° of theright twisting. On the other hand, the twisted angle in the thicknessdirection of the second optically-anisotropic layer was 80° of the lefttwisting.

In the cross-sectional SEM image of the liquid crystal diffractionelement, in the first optically-anisotropic layer and the secondoptically-anisotropic layer, bright and dark lines obliquely tilted withrespect to the normal line were observed. In addition, the tiltdirection of the bright and dark lines of the firstoptically-anisotropic layer with respect to the normal line was oppositeto that of the second optically-anisotropic layer. As described above,the normal line was the normal line of the interface between the firstoptically-anisotropic layer and the second optically-anisotropic layer.

In the first optically-anisotropic layer and the secondoptically-anisotropic layer, the tilt angle of the bright and dark lineswith respect to the normal line gradually decreased from the centertoward the outside. Further in the pattern of the bright and dark linesof the first optically-anisotropic layer and the secondoptically-anisotropic layer, a state where the period decreased from thecenter toward the outside was observed.

<Preparation of Light Deflection Device>

A light deflection device was prepared using the same method as that ofExample 2, except that the liquid crystal diffraction element waschanged to the liquid crystal diffraction element including twooptically-anisotropic layers of the first optically-anisotropic layerand the second optically-anisotropic layer.

Example 4

<Preparation of Liquid Crystal Diffraction Element>

As conceptually shown in FIG. 15 , a liquid crystal diffraction elementthree optically-anisotropic layers in which a thirdoptically-anisotropic layer was provided between the firstoptically-anisotropic layer and the second optically-anisotropic layerwas prepared.

The first optically-anisotropic layer and the secondoptically-anisotropic layer were layers in which the liquid crystalcompound was twisted and aligned. Therefore, the firstoptically-anisotropic layer and the second optically-anisotropic layerwere tilted optically-anisotropic layers in which the bright and darklines in the cross-sectional SEM image were tilted with respect to thenormal line as shown in FIG. 15 .

Further, the twisted direction in the twisted alignment of the liquidcrystal compound of the first optically-anisotropic layer was differentfrom that of the second optically-anisotropic layer. As a result, thetilt directions of the bright and dark lines derived from the twistedalignment in the cross-sectional SEM images were different from eachother.

On the other hand, the third optically-anisotropic layer disposedbetween the first optically-anisotropic layer and the secondoptically-anisotropic layer was a non-tilted optically-anisotropic layerin which the liquid crystal compound was not twisted and aligned and thebright and dark lines extended in the normal direction. As describedabove, the normal line was the normal line of the interface between thefirst optically-anisotropic layer and the second optically-anisotropiclayer.

As described above, the twisted direction in the twisted alignment ofthe liquid crystal compound of the first optically-anisotropic layer wasdifferent from that of the second optically-anisotropic layer. As aresult, the tilt directions of the bright and dark lines derived fromthe twisted alignment in the cross-sectional SEM images were differentfrom each other.

(Formation of First Optically-Anisotropic Layer)

As the liquid crystal composition forming the firstoptically-anisotropic layer, the following composition A-7 was prepared.

Composition A-7

Liquid crystal compound L-1 100.00 parts by mass Chiral agent A 0.19parts by mass Polymerization initiator (IRGACURE 3.00 parts by mass(registered trade name) 907, manufactured by BASF SE) Photosensitizer(KAYACURE DETX-S, 1.00 part by mass manufactured by Nippon Kayaku Co.,Ltd.) Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2840.00parts by mass

A first optically-anisotropic layer was formed on the alignment film P-1using the same method as that of the optically-anisotropic layeraccording to Example 1, except that the composition A-7 was used.

(Formation of Third Optically-Anisotropic Layer)

The third optically-anisotropic layer 3 was formed on the firstoptically-anisotropic layer by applying the above-described compositionA-1 using the same method as that of the optically-anisotropic layeraccording to Example 1, except that the thickness was changed.

Formation of Second Optically-Anisotropic Layer)

As the liquid crystal composition forming the secondoptically-anisotropic layer, the following composition A-8 was prepared.

Composition A-8

Liquid crystal compound L-1 100.00 parts by mass Chiral agent B 0.32parts by mass Polymerization initiator (IRGACURE 3.00 parts by mass(registered trade name) 907, manufactured by BASF SE) Photosensitizer(KAYACURE DETX-S, 1.00 part by mass manufactured by Nippon Kayaku Co.,Ltd.) Leveling agent T-1 0.08 parts by mass Methyl ethyl ketone 2840.00parts by mass

A second optically-anisotropic layer was formed on the thirdoptically-anisotropic layer using the same method as that of theoptically-anisotropic layer according to Example 1, except that thecomposition A-8 was used. As a result, a liquid crystal diffractionelement including three optically-anisotropic layers as shown in FIG. 15was prepared.

In the prepared liquid crystal diffraction element, in the firstoptically-anisotropic layer and the second optically-anisotropic layer,finally, Δn₉₄₀×Thickness (Re(940)) of the liquid crystal was 470 nm, andin the third optically-anisotropic layer, Δn₉₄₀×Thickness (Re(940)) ofthe liquid crystal was 564 nm.

In the first optically-anisotropic layer, the secondoptically-anisotropic layer, and the third optically-anisotropic layer,a periodic liquid crystal alignment pattern having a concentric circularshape as shown in FIG. 10 was provided. Further it was verified with apolarizing microscope that the rotation period of the optical axis ofthe liquid crystal compound gradually decreased from the center towardthe outside in the in-plane direction in which the optical axis rotatedand that the rotation direction of the optical axis was reversed at thecenter.

In the horizontal rotation alignment pattern of the firstoptically-anisotropic layer, regarding the rotation period (singleperiod) over which the optical axis of the liquid crystal compoundrotated by 180°, the rotation period of a center portion wassignificantly large (the inverse of the rotation period was considered0), the rotation period of a portion at a distance of 1.0 mm from thecenter was 9.0 μm, the rotation period of a portion at a distance of 2.5mm from the center was 4.5 μm, and the rotation period of a portion at adistance of 4.0 mm from the center was 3.0 μm. This way, the rotationperiod gradually decreased from the center toward the outer direction.

Further, the twisted direction in the liquid crystal compound of thefirst optically-anisotropic layer was opposite to that of the secondoptically-anisotropic layer. In addition, the twisted angle of the firstoptically-anisotropic layer in the thickness direction was 130° of theright twisting. The twisted angle of the third optically-anisotropiclayer in the thickness direction was 0°. The twisted angle of the secondoptically-anisotropic layer in the thickness direction was 130° of theleft twisting.

In the cross-sectional SEM image of the liquid crystal diffractionelement, in the first optically-anisotropic layer and the secondoptically-anisotropic layer, bright and dark lines obliquely tilted withrespect to the normal line were observed. In the thirdoptically-anisotropic layer, bright and dark lines extending along thenormal were observed along the normal line. The tilt direction of thebright and dark lines of the first optically-anisotropic layer withrespect to the normal line was opposite to that of the secondoptically-anisotropic layer. As described above, the normal line was thenormal line of the interface between the first optically-anisotropiclayer and the second optically-anisotropic layer.

In the first optically-anisotropic layer and the secondoptically-anisotropic layer, the tilt angle of the bright and dark lineswith respect to the normal line gradually decreased from the centertoward the outside. Further in the pattern of the bright and dark linesof the first optically-anisotropic layer and the secondoptically-anisotropic layer, a state where the period decreased from thecenter toward the outside was observed.

<Preparation of Light Deflection Device>

A light deflection device was prepared using the same method as that ofExample 2, except that the liquid crystal diffraction element waschanged to the liquid crystal diffraction element including threeoptically-anisotropic layers of the first optically-anisotropic layer,the second optically-anisotropic layer, and the thirdoptically-anisotropic layer.

[Evaluation]

Regarding the light deflection device according to Examples 3 and 4, theemission angle from the liquid crystal diffraction element was measuredand evaluated using the same method as that of Example 1.

In the evaluation, likewise, it was verified that the deflection anglefrom the micromirror device was largely extended from an incidence anglerange of −35° to 35° by the liquid crystal diffraction element, and thelight was emitted at a deflection angle of about ±70°. In addition, inExample 3 rather than Example 2, or in Example 4, strong emitted lightwas obtained in a wider angle range.

In addition, in light deflection devices according to Examples 3 and 4,a larger amount of deflected light that in the light deflection deviceaccording to Example 1 was able to be emitted.

Other Examples

Further, light deflection devices were prepared by using the hologramsheet described in JP2016-184124A, a surface relief diffraction elementincluding a relief pattern formed using the same method as that of apolymer banknote described in JP2015-093439A, and a diffraction elementusing fine patterning of an inorganic material described inJP2017-111277A as the diffraction element instead of the liquid crystaldiffraction element. In the diffraction element, the periodic structurepitch gradually changed such that the diffraction angle graduallyincreased from the center of deflection (deflection orientation) fromthe liquid crystal optical phase modulation element toward both ends.

As a result, even in a case where any one of the diffraction elementswas used, it was verified that the deflection angle from the liquidcrystal optical phase modulation element was largely extended by thehologram sheet, the surface relief diffraction element, or thediffraction element using fine patterning of the inorganic material.

As described above, it was verified that the present invention canexhibit an effect of obtaining a light deflection device having a simplestructure suitable for reducing the size and weight where a deflectionangle can be increased.

INDUSTRIAL APPLICABILITY

The present invention is suitably applicable to various optical devicessuch as a distance-measuring sensor.

EXPLANATION OF REFERENCES

-   -   12: support    -   13: alignment film    -   14, 14A: optically-anisotropic layer    -   20: liquid crystal compound    -   22: optical axis    -   24: equiphase surface    -   50, 80: exposure device    -   52, 82: laser    -   54, 84: light source    -   56: beam splitter    -   58A, 58B, 90A, 90B: mirror    -   60A, 60B, 96, 111: λ/4 plate    -   70: laser light    -   72A, 72B: beam    -   86, 94: polarization beam splitter    -   92: lens    -   100: light deflection device    -   101: liquid crystal optical phase modulation element    -   101A: light deflection element    -   102: interval    -   103: incidence surface    -   110: optical device    -   112: light source    -   114: light-receiving element    -   121, 121A, 220, 224: liquid crystal diffraction element    -   131: collecting lens    -   132: MEMS light deflection element    -   134, 141: drive unit    -   151: incidence light    -   161: emission surface    -   171: arrow    -   201: first transparent substrate    -   203: second transparent substrate    -   207: director    -   209: alignment layer    -   211: composite electrode    -   213: common electrode    -   215: first optically-anisotropic layer    -   216: second optically-anisotropic layer    -   219: third optically-anisotropic layer    -   501: nematic liquid crystal layer    -   L: light    -   light L₁, L₄₁: incidence light    -   L₂, L₄₂, L₄₃; emitted light    -   P_(O): linearly polarized light    -   P_(R): right circularly polarized light    -   P_(L): left circularly polarized light    -   M: laser light    -   MP: P polarized light    -   MS: S polarized light

What is claimed is:
 1. A light deflection device comprising: a lightdeflection element that deflects incident light to be emitted; a drivingunit that drives the light deflection element; a liquid crystaldiffraction element that is disposed on a light emission side of thelight deflection element in which a periodic structure pitch graduallychanges from a center of deflection from the light deflection elementtoward an outside, the periodic structure pitch being 0.5 to 5 μm; and alight collecting element that is provided upstream of the liquid crystaldiffraction element in a light traveling direction, wherein the liquidcrystal diffraction element includes at least threeoptically-anisotropic layers each of which is formed using a compositionincluding a liquid crystal compound and has a liquid crystal alignmentpattern in which a direction of an optical axis derived from the liquidcrystal compound changes while continuously rotating in at least onein-plane direction, two optically-anisotropic layers of the at leastthree optically-anisotropic layers each include a liquid crystalcompound that is twisted and aligned along a helical axis extending in athickness direction, and have opposite twisted directions in which theliquid crystal compound is twisted and aligned along the helical axisextending in the thickness direction, remaining oneoptically-anisotropic layer of the at least three optically-anisotropiclayers is the optically-anisotropic layer in which the liquid crystalcompound is not twisted and aligned, and is disposed between the twooptically-anisotropic layers in which the liquid crystal compound istwisted and aligned, the periodic structure pitch of the liquid crystaldiffraction element gradually decreases from the center of deflectionfrom the light deflection element toward the outside, and the lightcollecting element converts light emitted from the liquid crystaldiffraction element into parallel light by reducing a diameter of lightincident on the liquid crystal diffraction element.
 2. The lightdeflection device according to claim 1, wherein the light deflectionelement is a liquid crystal optical phase modulation element.
 3. Thelight deflection device according to claim 1, wherein the lightdeflection element is a MEMS light deflection element.
 4. The lightdeflection device according to claim 1, wherein the liquid crystalalignment pattern of the optically-anisotropic layer is a concentriccircular pattern having a concentric circular shape where the in-planedirection in which the direction of the optical axis derived from theliquid crystal compound changes while continuously rotating moves froman inside toward an outside.
 5. The light deflection device according toclaim 1, comprising: a λ/4 plate.
 6. The light deflection deviceaccording to claim 5, wherein the λ/4 plate is provided between thelight deflection element and the liquid crystal diffraction element. 7.The light deflection device according to claim 1, wherein the lightcollecting element is provided upstream of the light deflection elementin the light traveling direction.
 8. An optical device comprising: thelight deflection device according to claim 1; a light source that emitslight to the light deflection element of the light deflection device;and a light-receiving element.